Database Solutions

DATABASE SOLUTIONS (2nd Edition) doubting Thomas M CONNOLLY & CAROLYN E BEGG SOLUTIONS TO REVIEW QUESTIONS Chapter 1 Introduction- Re medical prognosis questions 1. 1List four fictitious charactersetters cases of entropy purse ca lend starselfs se compargonate than those listed in constituent 1. 1. Some examples could be A frame that important(prenominal)tains parting part elaborate for a car manufacturer An advertising teleph bingler keeping details of in t expose ensemble lymph glands and adverts placed with them A training confederation keeping course training and participants details An organization primary(prenominal)taining every last(predicate) in al star gross r flatue mark in orderion. 1. 2Discuss the meaning of to to each one one(prenominal) of the pursual enclosures (a) entropyFor end blend inrs, this constitutes all(a) the incompatible set connected with the various marks/entities that atomic look 18 of c at a timern to them. (b) inf obase A appointd collection of lumberically related in phaseation (and a rendering of this information), traffic patterned to meet the randomness admits of an organization. (c)database forethought agreement A softwargon package program go alongs that en sui circumvents drug substance ab substance ab habitrs to define, make water, and maintain the database and digests controlled door to this database. (d) practise program A computing device program that interacts with the database by issuing an withdraw request (typically an SQL disputation) to the database management ashes. (e)data independenceThis is essentially the disengagement of underlying data file twists from the programs that operate on them, as well called program-data independence. (f) ensures. A practical(prenominal) h elderly over that does non of necessity exist in the database nevertheless is generated by the database management system from the underlying base accedes whenever its access ed. These present alone a subset of the database that is of fussy interest to a exploiter. moots prat be customized, for example, field label whitethorn change, and they also try a level of protection preventing drug hotshot-valued functionrs from perceive certain data. 1. 3Describe the main characteristics of the database burn up.Focus is now on the data archetypal, and hence the applications. The structure of the data is now kept separate from the programs that operate on the data. This is held in the governing body cata lumber or data dictionary. Programs piece of tail now sh ar data, which is no wanter fragmented. in that respect is also a reduction in redundancy, and achievement of program-data independence. 1. 4Describe the five comp iodinents of the DBMS surroundings and discuss how they relate to each various. (1)Hardw atomic number 18The calculator organisation(s) that the DBMS and the application programs run for on. This can range from a unitar y PC, to a adept mainframe, to a ne 2rk of computers. 2)Softw atomic number 18The DBMS computer softwargon product and the application programs, together with the operating musical parade, including ne twork softw atomic number 18 if the DBMS is be employ over a network. (3) in workationThe data acts as a couplet amidst the computer ironwargon and software components and the human components. As weve al stool give tongue to, the database contains twain the operational data and the meta-data (the data virtually data). (4)ProceduresThe instructions and rules that restrain the trope and use of the database. This whitethorn acknowledge instructions on how to log on to the DBMS, make clientele copies of the database, and how to handle hardware or software failures. 5)PeopleThis includes the database useers, database administrators (DBAs), application programmers, and the end-users. 1. 5Describe the problems with the traditional two-tier client- emcee architecture and discuss how these problems were overcome with the three-tier client-server architecture. In the mid-1990s, as applications became to a greater extent complex and potentially could be deployed to hundreds or thousands of end-users, the client stead of this architecture gave rise to two problems A fat client, requiring considerable re starts on the clients computer to run in effect (re semens include harrow space, RAM, and CPU power). A solid client side administration overhead. By 1995, a bleak variation of the traditional two-tier client-server feigning appeared to solve these problems called the three-tier client-server architecture. This new-fangled architecture proposed three layers, each potentially running on a different platform (1)The user embrasure layer, which runs on the end-users computer (the client). (2)The vexation logic and data condition outing layer. This place tier runs on a server and is practically called the application server. One application server is initiationed to serve quadruplex clients. (3)A DBMS, which bloods the data infallible by the middle tier.This tier whitethorn run on a separate server called the database server. The three-tier spirit has much a(prenominal) advantages over the traditional two-tier bod, much(prenominal) as A minute client, which requires less expensive hardware. Simplified application maintenance, as a result of centralizing the stock logic for m both end-users into a hotshot application server. This eliminates the concerns of software distri exactlyion that are problematic in the traditional two-tier client-server architecture. Added modularity, which makes it easier to modify or replace one tier without disturbing the opposite tiers. Easier load balancing, a reach as a result of separating the core duty logic from the database agencys. For example, a Transaction Processing Monitor (TPM) can be used to reduce the number of connections to the database server. (A TPM is a progra m that controls data depute surrounded by clients and servers in order to provide a consistent environment for Online Transaction Processing (OLTP). ) An additional advantage is that the three-tier architecture maps quite of course to the Web environment, with a Web browser acting as the thin client, and a Web server acting as the application server.The three-tier client server architecture is expoundd in envision 1. 4. 1. 6Describe the functions that should be provided by a modern full-scale multi-user DBMS. Data Storage, Retrieval and Update warrant Services A spendr-Accessible CatalogSupport for Data discourse Transaction SupportIntegrity Services Concurrency Control ServicesServices to Promote Data emancipation Recovery ServicesUtility Services 1. 7Of the functions described in your answer to Question 1. 6, which ones do you think would non be needed in a standalone PC DBMS? can justification for your answer.Concurrency Control Services only atomic number 53 user. Au thorization Services only individual(a) user, but may be needed if different individuals are to use the DBMS at different times. Utility Services limited in scope. Support for Data Communication only standalone constitution of rules. 1. 8Discuss the advantages and disadvantages of DBMSs. Some advantages of the database plan of attack include control of data redundancy, data consistency, sharing of data, and improved security and bingle. Some disadvantages include complexity, cost, reduced functioning, and high impact of a failure.Chapter 2 The Relational Model Re entrance questions 2. 1Discuss each of the pursual concepts in the context of the relational data model (a)relation A control board with tugs and rows. (b) property A get upd tug of a relation. (c)domain The set of forfei plank values for one or more attributes. (d)tuple A drop off of a relation. (e)relational database. A collection of generalized put overs. 2. 2Discuss the properties of a relational table. A relational table has the interest properties The table has a name that is distinct from all other tables in the database. all(prenominal) cell of the table contains exactly one value. For example, it would be aggrieve to store several(prenominal) telephone numbers for a virtuoso pitchfork in a single cell. In other words, tables dont contain repeating groups of data. A relational table that satisfies this property is said to be regulationized or in front conventionality form. ) Each tug has a distinct name. The values of a column are all from the resembling domain. The order of columns has no significance. In other words, provided a column name is ranged along with the column values, we can interchange columns. Each record is distinct thither are no duplicate records. The order of records has no significance, theoretically. 2. 3Discuss the differences between the medical prognosis primevals and the main(a) winder of a table. justify what is meant by a forei gn tombstone. How do foreign keys of tables relate to candidate keys? Give examples to illustrate your answer. The patriarchal key is the candidate key that is selected to secern tuples uniquely at bottom a relation. A foreign key is an attribute or set of attributes within one relation that accordes the candidate key of some (possibly the equivalent) relation. 2. 4What does a null fight d deliver?Represents a value for a column that is currently unknown or is non applicable for this record. 2. 5Define the two principal virtue rules for the relational model. Discuss why it is desirable to put finished these rules. Entity integrityIn a base table, no column of a primary key can be null. Referential integrityIf a foreign key exists in a table, either the foreign key value moldiness match a candidate key value of some record in its home table or the foreign key value moldiness be wholly null. Chapter 3 SQL and QBE analyze questions 3. 1What are the two study components o f SQL and what function do they serve?A data definition run-in (DDL) for defining the database structure. A data manipulation language (DML) for retrieving and updating data. 3. 2Explain the function of each of the clauses in the consider statement. What restrictions are imposed on these clauses? FROMspecifies the table or tables to be used WHEREfilters the rows subject to some condition drove BYforms groups of rows with the same column value HAVINGfilters the groups subject to some condition destinespecifies which columns are to appear in the output ORDER BYspecifies the order of the output. 3. What restrictions apply to the use of the nub functions within the SELECT statement? How do nulls affect the aggregate functions? An aggregate function can be used only in the SELECT list and in the HAVING clause. Apart from COUNT(*), each function eliminates nulls first and operates only on the remaining non-null values. COUNT(*) counts all the rows of a table, regardless of whether n ulls or duplicate values lead. 3. 4Explain how the GROUP BY clause kit and caboodle. What is the difference between the WHERE and HAVING clauses? SQL first applies the WHERE clause. Then it abstractly arranges he table based on the grouping column(s). Next, applies the HAVING clause and finally orders the result fit to the ORDER BY clause. WHERE filters rows subject to some condition HAVING filters groups subject to some condition. 3. 5What is the difference between a subquery and a join? Under what circumstances would you not be able to use a subquery? With a subquery, the columns specify in the SELECT list are restricted to one table. Thus, cannot use a subquery if the SELECT list contains columns from more than one table. 3. 6What is QBE and what is the kin between QBE and SQL?QBE is an alternative, in writing(p)-based, point-and-click way of life of querying the database, which is curiously suited for queries that are not too complex, and can be evince in terms of a fe w tables. QBE has acquired the reputation of cosmos one of the easiest ways for non-technical users to obtain information from the database. QBE queries are converted into their equivalent SQL statements in advance trans charge to the DBMS server. Chapter 4 Database Systems Development Lifecycle Re catch up with questions 4. 1Describe what is meant by the term software crisis.The past few decades has witnessed the dramatic rise in the number of software applications. M any(prenominal) of these applications proved to be demanding, requiring constant maintenance. This maintenance baffling correcting faults, implementing new user requirements, and modifying the software to run on new or upgraded platforms. With so much software around to support, the effort spent on maintenance began to absorb resources at an alarming rate. As a result, many major software projects were late, over budget, and the software produced was unreliable, difficult to maintain, and performed poorly.This led to what has croak known as the software crisis. Although this term was first used in the late 1960s, more than 30 years ulterior, the crisis is still with us. As a result, some stack now refer to the software crisis as the software depression. 4. 2Discuss the family consanguinity between the information organisations lifecycle and the database transcription maturation lifecycle. An information system is the resources that enable the collection, management, control, and dissemination of data/information without a company. The database is a fundamental component of an information system.The lifecycle of an information system is inherently linked to the lifecycle of the database that supports it. Typically, the points of the information systems lifecycle include planning, requirements collection and psychoanalysis, architectural plan (including database design), prototyping, implementation, runnel, conversion, and operational maintenance. As a database is a fundamental c omponent of the spectacularr company-wide information system, the database system instruction lifecycle is inherently linked with the information systems lifecycle. 4. 3in short describe the stages of the database system knowledge lifecycle. front trope 4. Stages of the database system ripening lifecycle. Database planning is the management activities that allow the stages of the database system development lifecycle to be realized as efficiently and efficaciously as possible. System definition involves puting the scope and boundaries of the database system including its major user bewitchs. A user view can aimplay a line of production line function or business application area. Requirements collection and analysis is the figure out of collecting and analyzing information around the company that is to be supported by the database system, and apply this information to determine the requirements for the new system.There are three onward motiones to relations with m ultiple user views, namely the modify admittance, the view integrating apostrophize, and a combination of twain. The centralized approach involves collating the users requirements for different user views into a single list of requirements. A data model representing all the user views is created during the database design stage. The view integration approach involves loss the users requirements for each user view as separate lists of requirements. Data models representing each user view are created and whence interconnected at a posterior stage of database design.Database design is the process of creating a design that will support the companys agency statement and committal objectives for the required database. This stage includes the discursive and fleshly design of the database. The aim of DBMS selection is to select a system that meets the current and future requirements of the company, balanced against costs that include the purchase of the DBMS product and any ad ditional software/hardware, and the costs associated with changeover and training. screening design involves blueprint the user interface and the application programs that use and process the database.This stage involves two main activities transaction design and user interface design. Prototyping involves prepareing a working model of the database system, which allows the agents or users to visualize and measure out the system. Implementation is the carnal realization of the database and application designs. Data conversion and commitment involves transferring any existing data into the new database and converting any existing applications to run on the new database. Testing is the process of running the database system with the objective of finding mistakes.Operational maintenance is the process of monitoring and maintaining the system following installation. 4. 4Describe the drive of creating a mission statement and mission objectives for the required database during t he database planning stage. The mission statement defines the major aims of the database system, while each mission objective identifies a extra task that the database essential support. 4. 5Discuss what a user view represents when scheming a database system. A user view defines what is required of a database system from the perspective of a point job ( such as Manager orSupervisor) or business application area (such as marketing, personnel, or stock control). 4. 6Compare and secernate the centralized approach and view integration approach to managing the design of a database system with multiple user views. An important activity of the requirements collection and analysis stage is deciding how to deal with the feature where there is more than one user view. There are three approaches to dealing with multiple user views the centralized approach, the view integration approach, and a combination of both approaches.Centralized approach Requirements for each user view are merged i nto a single list of requirements for the new database system. A rational data model representing all user views is created during the database design stage. The centralized approach involves collating the requirements for different user views into a single list of requirements. A data model representing all user views is created in the database design stage. A diagram representing the management of user views 1 to 3 use the centralized approach is recordn in view 4. 4.Generally, this approach is preferred when there is a significant overlap in requirements for each user view and the database system is not overly complex. See Figure 4. 4 The centralized approach to managing multiple user views 1 to 3. View integration approach Requirements for each user view remain as separate lists. Data models representing each user view are created and thus merged later during the database design stage. The view integration approach involves leaving the requirements for each user view as sep arate lists of requirements.We create data models representing each user view. A data model that represents a single user view is called a local logical data model. We thence merge the local data models to create a global logical data model representing all user views of the company. A diagram representing the management of user views 1 to 3 using the view integration approach is shown in Figure 4. 5. Generally, this approach is preferred when there are significant differences between user views and the database system is sufficiently complex to justify dividing the work into more manageable parts.See Figure 4. 5 The view integration approach to managing multiple user views 1 to 3. For some complex database systems it may be allow to use a combination of both the centralized and view integration approaches to managing multiple user views. For example, the requirements for two or more users views may be first merged using the centralized approach and then used to create a local logi cal data model. ( thence in this situation the local data model represents not just a single user view but the number of user views merged using the centralized approach).The local data models representing one or more user views are then merged using the view integration approach to form the global logical data model representing all user views. 4. 7Explain why it is needful to select the can DBMS forward beginning the natural database design phase. Database design is made up of two main phases called logical and physical design. During logical database design, we recognize the important objects that need to be represented in the database and the descents between these objects.During physical database design, we go down how the logical design is to be physically implemented (as tables) in the target DBMS. Therefore it is necessary to have selected the target DBMS before we are able to proceed to physical database design. See Figure 4. 1 Stages of the database system developme nt lifecycle. 4. 8Discuss the two main activities associated with application design. The database and application design stages are tally activities of the database system development lifecycle. In well-nigh cases, we cannot complete the application design until the design of the database itself has taken place.On the other hand, the database exists to support the applications, and so there must(prenominal) be a flow of information between application design and database design. The two main activities associated with the application design stage is the design of the user interface and the application programs that use and process the database. We must ensure that all the functionality stated in the requirements judicial admissions is present in the application design for the database system. This involves bearing the interaction between the user and the data, which we call transaction design.In addition to designing how the required functionality is to be achieved, we have to design an appropriate user interface to the database system. 4. 9Describe the potential benefits of developing a prototype database system. The conclusion of developing a prototype database system is to allow users to use the prototype to position the features of the system that work well, or are inadequate, and if possible to suggest improvements or even new features for the database system. In this way, we can greatly clarify the requirements and evaluate the feasibility of a busy system design.Prototypes should have the major advantage of cosmosness relatively inexpensive and quick to build. 4. 10Discuss the main activities associated with the implementation stage. The database implementation is achieved using the Data Definition Language (DDL) of the selected DBMS or a graphical user interface (GUI), which provides the same functionality while hiding the low-level DDL statements. The DDL statements are used to create the database structures and empty database files. Any specified user views are also implemented at this stage.The application programs are implemented using the preferred third or fourth generation language (3GL or 4GL). Parts of these application programs are the database transactions, which we implement using the Data consumption Language (DML) of the target DBMS, possibly embedded within a host programming language, such as Visual Basic (VB), VB. net, Python, Delphi, C, C++, C, Java, COBOL, Fortran, Ada, or Pascal. We also implement the other components of the application design such as menu screens, data entry forms, and reports.Again, the target DBMS may have its own fourth generation tools that allow rapid development of applications by means of the provision of non-procedural query languages, reports generators, forms generators, and application generators. Security and integrity controls for the application are also implemented. Some of these controls are implemented using the DDL, but others may need to be defined outside t he DDL using, for example, the supplied DBMS utilities or operating system controls. 4. 11Describe the purpose of the data conversion and loading stage.This stage is required only when a new database system is replacing an old system. Nowadays, its common for a DBMS to have a advantage that loads existing files into the new database. The utility usually requires the specification of the source file and the target database, and then automatically converts the data to the required format of the new database files. Where applicable, it may be possible for the developer to convert and use application programs from the old system for use by the new system. 4. 2Explain the purpose of exam the database system. Before going live, the newly developed database system should be well tested. This is achieved using carefully planned test strategies and realistic data so that the entire test process is methodically and rigorously carried out. Note that in our definition of testing we have not used the commonly held view that testing is the process of demonstrating that faults are not present. In fact, testing cannot show the absence of faults it can show only that software faults are present.If testing is conducted winnerfully, it will uncover errors in the application programs and possibly the database structure. As a certifyary benefit, testing demonstrates that the database and the application programs appear to be working according to their specification and that performance requirements appear to be satisfied. In addition, metrics quiet from the testing stage provides a measure of software reliability and software quality. As with database design, the users of the new system should be involved in the testing process.The ideal situation for system testing is to have a test database on a separate hardware system, but often this is not available. If real data is to be used, it is essential to have backups taken in case of error. Testing should also cover usability of the database system. Ideally, an evaluation should be conducted against a usability specification. Examples of criteria that can be used to conduct the evaluation include (Sommerville, 2000) Learnability How long does it take a new user to become productive with the system? Performance How well does the system response match the users work practice? Robustness How tolerant is the system of user error? Recoverability How good is the system at recovering from user errors? Adapatability How closely is the system tied to a single model of work? Some of these criteria may be evaluated in other stages of the lifecycle. After testing is complete, the database system is ready to be signed off and handed over to the users. 4. 13What are the main activities associated with operational maintenance stage.In this stage, the database system now moves into a maintenance stage, which involves the following activities Monitoring the performance of the database system. If the performance fall s below an acceptable level, the database may need to be tuned or reorganized. Maintaining and upgrading the database system (when required). New requirements are incorporate into the database system through the preceding stages of the lifecycle. Chapter 5 Database Administration and Security Review questions 5. 1Define the purpose and tasks associated with data administration and database administration.Data administration is the management and control of the corporate data, including database planning, development and maintenance of standards, policies and procedures, and logical database design. Database administration is the management and control of the physical realization of the corporate database system, including physical database design and implementation, setting security and integrity controls, monitoring system performance, and reorganizing the database as necessary. 5. 2Compare and contrast the main tasks carried out by the DA and DBA.The Data Administrator (DA) and Database Administrator (DBA) are responsible for managing and exacting the activities associated with the corporate data and the corporate database, respectively. The DA is more concerned with the advance(prenominal) stages of the lifecycle, from planning through to logical database design. In contrast, the DBA is more concerned with the later stages, from application/physical database design to operational maintenance. Depending on the size and complexity of the organization and/or database system the DA and DBA can be the accountability of one or more people. . 3Explain the purpose and scope of database security. Security considerations do not only apply to the data held in a database. Breaches of security may affect other parts of the system, which may in change form affect the database. Consequently, database security encompasses hardware, software, people, and data. To effectively implement security requires appropriate controls, which are defined in specific mission objec tives for the system. This need for security, while often having been neglected or overlooked in the past, is now increasingly recognise by organizations.The reason for this turn-around is due to the increasing amounts of all important(p) corporate data macrocosm stored on computer and the acceptance that any loss or unavailability of this data could be potentially disastrous. 5. 4List the main types of threat that could affect a database system, and for each, describe the possible outcomes for an organization. Figure 5. 1 A compend of the potential threats to computer systems. 5. 5Explain the following in terms of providing security for a database authorization views backup and recovery integrity scratchion maraud. AuthorizationAuthorization is the granting of a pay off or privilege that enables a subject to have legitimate access to a system or a systems object. Authorization controls can be built into the software, and govern not only what database system or object a specif ied user can access, but also what the user may do with it. The process of authorization involves credential of a subject requesting access to an object, where subject represents a user or program and object represents a database table, view, procedure, trigger, or any other object that can be created within the database system. ViewsA view is a virtual table that does not necessarily exist in the database but can be produced upon request by a particular user, at the time of request. The view mechanism provides a powerful and flexible security mechanism by hiding parts of the database from certain users. The user is not aware of the humans of any columns or rows that are missing from the view. A view can be defined over several tables with a user being granted the appropriate privilege to use it, but not to use the base tables. In this way, using a view is more restricting than simply having certain privileges granted to a user on the base table(s).Backup and recovery Backup is the process of periodically taking a write of the database and log file (and possibly programs) onto offline remembering media. A DBMS should provide backup facilities to assist with the recovery of a database following failure. To keep line of database transactions, the DBMS maintains a particular(a) file called a log file (or journal) that contains information close to all updates to the database. It is always advisable to make backup copies of the database and log file at regular intervals and to ensure that the copies are in a bulletproof location.In the event of a failure that renders the database unusable, the backup double and the details captured in the log file are used to pay back the database to the latest possible consistent state. Journaling is the process of keeping and maintaining a log file (or journal) of all changes made to the database to enable recovery to be undertaken effectively in the event of a failure. Integrity constraints Contribute to maintaining a secure database system by preventing data from becoming invalid, and hence giving lead astray or incorrect results. EncryptionIs the encoding of the data by a special algorithm that renders the data unreadable by any program without the decipherment key. If a database system holds particularly sensitive data, it may be deemed necessary to encode it as a precaution against possible external threats or attempts to access it. Some DBMSs provide an encryption facility for this purpose. The DBMS can access the data (after decoding it), although there is degradation in performance because of the time taken to decode it. Encryption also protects data transmit over communication lines.There are a number of proficiencys for encoding data to conceal the information some are termed irreversible and others reversible. Irreversible techniques, as the name implies, do not permit the pilot burner data to be known. However, the data can be used to obtain valid statistical information. Revers ible techniques are more commonly used. To transmit data firmly over insecure networks requires the use of a cryptosystem, which includes an encryption key to encrypt the data (plaintext) an encryption algorithm that, with the encryption key, transforms the plain text into ciphertext a decipherment key to decrypt the ciphertext a decryption algorithm that, with the decryption key, transforms the ciphertext back into plain text. Redundant Array of In mutually beneficial dishs (RAID) RAID works by having a large disk array comprising an arrangement of several in hooked disks that are organized to improve reliability and at the same time increase performance. The hardware that the DBMS is running on must be fault-tolerant, meaning that the DBMS should continue to operate even if one of the hardware components fails. This suggests having redundant components that can be seamlessly integrated into the working system whenever there is one or more component failures.The main hardware co mponents that should be fault-tolerant include disk drives, disk controllers, CPU, power supplies, and cooling yellowish browns. Disk drives are the most vulnerable components with the shortest times between failures of any of the hardware components. One solution is the use of Redundant Array of Independent Disks (RAID) technology. RAID works by having a large disk array comprising an arrangement of several independent disks that are organized to improve reliability and at the same time increase performance. Chapter 6 Fact-Finding Review questions 6. Briefly describe what the process of investigative attempts to achieve for a database developer. Fact-finding is the stately process of using techniques such as interviews and questionnaires to collect facts about systems, requirements, and preferences. The database developer uses investigative techniques at various stages throughout the database systems lifecycle to capture the necessary facts to build the required database syste m. The necessary facts cover the business and the users of the database system, including the terminology, problems, opportunities, constraints, requirements, and priorities.These facts are captured using investigative techniques. 6. 2Describe how fact-finding is used throughout the stages of the database system development lifecycle. There are many occasions for fact-finding during the database system development lifecycle. However, fact-finding is particularly crucial to the early stages of the lifecycle, including the database planning, system definition, and requirements collection and analysis stages. Its during these early stages that the database developer learns about the terminology, problems, opportunities, constraints, requirements, and priorities of the business and the users of the system.Fact-finding is also used during database design and the later stages of the lifecycle, but to a lesser extent. For example, during physical database design, fact-finding becomes tech nical as the developer attempts to learn more about the DBMS selected for the database system. Also, during the final stage, operational maintenance, fact-finding is used to look on whether a system requires tuning to improve performance or tho developed to include new requirements. 6. 3For each stage of the database system development lifecycle identify examples of the facts captured and the documentation produced. . 4A database developer popularly uses several fact-finding techniques during a single database project. The five most commonly used techniques are examining documentation, interviewing, observing the business in operation, conducting research, and using questionnaires. Describe each fact-finding technique and identify the advantages and disadvantages of each. Examining documentation can be useful when youre trying to gain some insight as to how the need for a database arose.You may also find that documentation can be helpful to provide information on the business (or part of the business) associated with the problem. If the problem relates to the current system there should be documentation associated with that system. Examining documents, forms, reports, and files associated with the current system, is a good way to chop-chop gain some guessing of the system. Interviewing is the most commonly used, and frequently most useful, fact-finding technique. You can interview to collect information from individuals face-to-face.There can be several objectives to using interviewing such as finding out facts, checking facts, generating user interest and feelings of involvement, identifying requirements, and gathering ideas and opinions. Observation is one of the most effective fact-finding techniques you can use to understand a system. With this technique, you can either participate in, or watch a person perform activities to learn about the system. This technique is particularly useful when the validity of data collected through other methods is in q uestion or when the complexity of certain aspects of the system prevents a clear explanation by the end-users.A useful fact-finding technique is to research the application and problem. Computer trade journals, reference books, and the Internet are good sources of information. They can provide you with information on how others have puzzle out similar problems, plus you can learn whether or not software packages exist to solve your problem. Another fact-finding technique is to conduct surveys through questionnaires. Questionnaires are special-purpose documents that allow you to gather facts from a large number of people while maintaining some control over their responses.When dealing with a large audience, no other fact-finding technique can tabulate the same facts as efficiently. 6. 5Describe the purpose of defining a mission statement and mission objectives for a database system. The mission statement defines the major aims of the database system. Those driving the database proje ct within the business (such as the Director and/or owner) expressionly define the mission statement. A mission statement helps to clarify the purpose of the database project and provides a clearer path towards the efficient and effective creation of the required database system.Once the mission statement is defined, the next activity involves identifying the mission objectives. Each mission objective should identify a particular task that the database must support. The assumption is that if the database supports the mission objectives then the mission statement should be met. The mission statement and objectives may be accompanied with additional information that specifies, in general terms, the work to be done, the resources with which to do it, and the money to pay for it all. 6. 6What is the purpose of the systems definition stage?The purpose of the system definition stage is to identify the scope and boundary of the database system and its major user views. Defining the scope and boundary of the database system helps to identify the main types of data mentioned in the interviews and a rough guide as to how this data is related. A user view represents the requirements that should be supported by a database system as defined by a particular job role (such as Manager or Assistant) or business application area (such as video rentals or stock control). 6. How do the contents of a users requirements specification differ from a systems specification? There are two main documents created during the requirements collection and analysis stage, namely the users requirements specification and the systems specification. The users requirements specification describes in detail the data to be held in the database and how the data is to be used. The systems specification describes any features to be included in the database system such as the required performance and the levels of security. 6. Describe one approach to deciding whether to use centralized, view integratio n, or a combination of both when developing a database system for multiple user views. One way to help you make a decision whether to use the centralized, view integration, or a combination of both approaches to manage multiple user views is to run into the overlap in terms of the data used between the user views identified during the system definition stage. Its difficult to give hairsplitting rules as to when its appropriate to use the centralized or view integration approaches.As the database developer, you should base your decision on an assessment of the complexity of the database system and the degree of overlap between the various user views. However, whether you use the centralized or view integration approach or a pastiche of both to build the underlying database, ultimately you need to create the pilot program user views for the working database system. Chapter 7 Entity-Relationship Modeling Review questions 7. 1Describe what entities represent in an ER model and prov ide examples of entities with a physical or conceptual existence.Entity is a set of objects with the same properties, which are identified by a user or company as having an independent existence. Each object, which should be uniquely identifiable within the set, is called an entity fact. An entity has an independent existence and can represent objects with a physical (or real) existence or objects with a conceptual (or abstract) existence. 7. 2Describe what family relationships represent in an ER model and provide examples of unary, binary, and collar relationships.Relationship is a set of meaningful acquaintances among entities. As with entities, each necktie should be uniquely identifiable within the set. A uniquely identifiable association is called a relationship fact. Each relationship is given a name that describes its function. For example, the prole entity is associated with the Role entity through a relationship called Plays, and the Role entity is associated with th e pictorial matter entity through a relationship called Features. The entities involved in a particular relationship are referred to as participants.The number of participants in a relationship is called the degree and indicates the number of entities involved in a relationship. A relationship of degree one is called unary, which is commonly referred to as a recursive relationship. A unary relationship describes a relationship where the same entity records more than once in different roles. An example of a unary relationship is Supervises, which represents an association of faculty with a supervisor where the supervisor is also a constituent of staff.In other words, the staff entity participates twice in the Supervises relationship the first club as a supervisor, and the second participation as a piece of staff who is supervised (supervisee). See Figure 7. 5 for a diagrammatical authority of the Supervises relationship. A relationship of degree two is called binary. A relati onship of a degree higher than binary is called a complex relationship. A relationship of degree three is called ternary. An example of a ternary relationship is Registers with three participating entities, namely Branch, faculty, and Member.The purpose of this relationship is to represent the situation where a portion of staff registers a element at a particular part, allowing for members to register at more than one severalize, and members of staff to move between tell apartes. Figure 7. 4 Example of a ternary relationship called Registers. 7. 3Describe what attributes represent in an ER model and provide examples of simple, composite, single-value, multi-value, and derived attributes. An attribute is a property of an entity or a relationship. Attributes represent what we want to know about entities.For example, a Video entity may be described by the catalogNo, title, category, dailyRental, and set attributes. These attributes hold values that describe each video fleetrenc e, and represent the main source of data stored in the database. Simple attribute is an attribute composed of a single component. Simple attributes cannot be further subdivided. Examples of simple attributes include the category and price attributes for a video. Composite attribute is an attribute composed of multiple components. Composite attributes can be further divided to have smaller components with an independent existence.For example, the name attribute of the Member entity with the value accept Nelson can be subdivided into fName (Don) and lName (Nelson). Single-valued attribute is an attribute that holds a single value for an entity go onrence. The majority of attributes are single-valued for a particular entity. For example, each occurrence of the Video entity has a single-value for the catalogNo attribute (for example, 207132), and because the catalogNo attribute is referred to as being single-valued. Multi-valued attribute is an attribute that holds multiple values for an entity occurrence.Some attributes have multiple values for a particular entity. For example, each occurrence of the Video entity may have multiple values for the category attribute (for example, Children and Comedy), and therefore the category attribute in this case would be multivalent. A multi-valued attribute may have a set of values with specified lower and upper limits. For example, the category attribute may have between one and three values. Derived attribute is an attribute that represents a value that is derivable from the value of a related attribute, or set of attributes, not necessarily in the same entity.Some attributes may be related for a particular entity. For example, the age of a member of staff (age) is derivable from the date of bear (DOB) attribute, and therefore the age and DOB attributes are related. We refer to the age attribute as a derived attribute, the value of which is derived from the DOB attribute. 7. 4Describe what multiplicity represents for a relationship. Multiplicity is the number of occurrences of one entity that may relate to a single occurrence of an associated entity. 7. 5What are business rules and how does multiplicity model these constraints?Multiplicity constrains the number of entity occurrences that relate to other entity occurrences through a particular relationship. Multiplicity is a representation of the policies established by the user or company, and is referred to as a business rule. Ensuring that all appropriate business rules are identified and represented is an important part of clay sculpture a company. The multiplicity for a binary relationship is generally referred to as one-to-one (11), one-to-many (1*), or many-to-many (**). Examples of three types of relationships include A member of staff manages a branch. A branch has members of staff. Actors play in videos. 7. 6How does multiplicity represent both the cardinality and the participation constraints on a relationship? Multiplicity really c onsists of two separate constraints known as cardinality and participation. Cardinality describes the number of possible relationships for each participating entity. Participation determines whether all or only some entity occurrences participate in a relationship. The cardinality of a binary relationship is what we have been referring to as one-to-one, one-to-many, and many-to-many.A participation constraint represents whether all entity occurrences are involved in a particular relationship (mandatory participation) or only some ( facultative participation). The cardinality and participation constraints for the Staff Manages Branch relationship are shown in Figure 7. 11. 7. 7Provide an example of a relationship with attributes. An example of a relationship with an attribute is the relationship called PlaysIn, which associates the Actor and Video entities. We may wish to record the character played by an actor in a given video.This information is associated with the PlaysIn relation ship quite an than the Actor or Video entities. We create an attribute called character to store this information and assign it to the PlaysIn relationship, as illustrated in Figure 7. 12. Note, in this figure the character attribute is shown using the symbol for an entity however, to distinguish between a relationship with an attribute and an entity, the rectangle representing the attribute is associated with the relationship using a hasten line. Figure 7. 12 A relationship called PlaysIn with an attribute called character. . 8Describe how reinforced and creaky entities differ and provide an example of each. We can classify entities as being either strong or faint-hearted. A strong entity is not dependent on the existence of another entity for its primary key. A unclouded entity is partly or wholly dependent on the existence of another entity, or entities, for its primary key. For example, as we can distinguish one actor from all other actors and one video from all other vid eos without the existence of any other entity, Actor and Video are referred to as being strong entities.In other words, the Actor and Video entities are strong because they have their own primary keys. An example of a weak entity called Role, which represents characters played by actors in videos. If we are unable to uniquely identify one Role entity occurrence from another without the existence of the Actor and Video entities, then Role is referred to as being a weak entity. In other words, the Role entity is weak because it has no primary key of its own. Figure 7. 6 Diagrammatic representation of attributes for the Video, Role, and Actor entities.Strong entities are sometimes referred to as parent, owner, or dominant entities and weak entities as child, dependent, or subordinate entities. 7. 9Describe how buff and chasm traps can occur in an ER model and how they can be firm. Fan and chasm traps are two types of connection traps that can occur in ER models. The traps normally oc cur due to a misinterpretation of the meaning of certain relationships. In general, to identify connection traps we must ensure that the meaning of a relationship (and the business rule that it represents) is fully understood and clearly defined.If we dont understand the relationships we may create a model that is not a square representation of the real world. A fan trap may occur when two entities have a 1* relationship that fan out from a third entity, but the two entities should have a direct relationship between them to provide the necessary information. A fan trap may be resolved through the addition of a direct relationship between the two entities that were originally separated by the third entity. A chasm trap may occur when an ER model suggests the existence of a relationship between entities, but the avenue does not exist between certain entity occurrences.More specifically, a chasm trap may occur where there is a relationship with optional participation that forms part of the pathway between the entities that are related. Again, a chasm trap may be resolved by the addition of a direct relationship between the two entities that were originally related through a pathway that included optional participation. Chapter 8 Normalization Review questions 8. 1Discuss how normalization may be used in database design. Normalization can be used in database design in two ways the first is to use ormalization as a bottom-up approach to database design the second is to use normalization in conjunction with ER modeling. Using normalization as a bottom-up approach involves analyzing the associations between attributes and, based on this analysis, grouping the attributes together to form tables that represent entities and relationships. However, this approach becomes difficult with a large number of attributes, where its difficult to establish all the important associations between the attributes. Alternatively, you can use a top-down approach to database design.In this approach, we use ER modeling to create a data model that represents the main entities and relationships. We then translate the ER model into a set of tables that represents this data. Its at this point that we use normalization to check whether the tables are well designed. 8. 2Describe the types of update anomalies that may occur on a table that has redundant data. Tables that have redundant data may have problems called update anomalies, which are classified as insertion, deletion, or modification anomalies. See Figure 8. 2 for an example of a table with redundant data called StaffBranch.There are two main types of insertion anomalies, which we illustrate using this table. Insertion anomalies (1)To insert the details of a new member of staff located at a given branch into the StaffBranch table, we must also unload the correct details for that branch. For example, to insert the details of a new member of staff at branch B002, we must wear the correct details of branch B002 so that the branch details are consistent with values for branch B002 in other records of the StaffBranch table. The data shown in the StaffBranch table is also shown in the Staff and Branch tables shown in Figure 8. 1.These tables do have redundant data and do not bide from this potential inconsistency, because for each staff member we only enter the appropriate branch number into the Staff table. In addition, the details of branch B002 are recorded only once in the database as a single record in the Branch table. (2)To insert details of a new branch that currently has no members of staff into the StaffBranch table, its necessary to enter nulls into the staff-related columns, such as staffNo. However, as staffNo is the primary key for the StaffBranch table, attempting to enter nulls for staffNo violates entity integrity, and is not allowed.The design of the tables shown in Figure 8. 1 avoids this problem because new branch details are entered into the Branch table separately from the staff details. The details of staff ultimately located at a new branch can be entered into the Staff table at a later date. Deletion anomalies If we delete a record from the StaffBranch table that represents the last member of staff located at a branch, the details about that branch are also lost from the database. For example, if we delete the record for staff graphics Peters (S0415) from the StaffBranch table, the details relating to branch B003 are lost from the database.The design of the tables in Figure 8. 1 avoids this problem because branch records are stored separately from staff records and only the column branchNo relates the two tables. If we delete the record for staff Art Peters (S0415) from the Staff table, the details on branch B003 in the Branch table remain unaffected. Modification anomalies If we want to change the value of one of the columns of a particular branch in the StaffBranch table, for example the telephone number for branch B001, we must update the re cords of all staff located at that branch.If this modification is not carried out on all the appropriate records of the StaffBranch table, the database will become inconsistent. In this example, branch B001 would have different telephone numbers in different staff records. The above examples illustrate that the Staff and Branch tables of Figure 8. 1 have more desirable properties than the StaffBranch table of Figure 8. 2. In the following sections, we examine how normal forms can be used to formalize the appellation of tables that have desirable properties from those that may potentially suffer from update anomalies. . 3Describe the characteristics of a table that violates first normal form (1NF) and then describe how such a table is converted to 1NF. The rule for first normal form (1NF) is a table in which the intersection of every column and record contains only one value. In other words a table that contains more than one atomic value in the intersection of one or more column for one or more records is not in 1NF. The non 1NF table can be converted to 1NF by restructuring original table by removing the column with the multi-values along with a copy of the primary key to create a new table.See Figure 8. 4 for an example of this approach. The advantage of this approach is that the resultant tables may be in normal forms later that 1NF. 8. 4What is the minimal normal form that a relation must satisfy? Provide a definition for this normal form. Only first normal form (1NF) is critical in creating appropriate tables for relational databases. in all the subsequent normal forms are optional. However, to avoid the update anomalies discussed in separate 8. 2, its normally recommended that you proceed to third normal form (3NF).First normal form (1NF) is a table in which the intersection of every column and record contains only one value. 8. 5Describe an approach to converting a first normal form (1NF) table to second normal form (2NF) table(s). second gear normal form applies only to tables with composite primary keys, that is, tables with a primary key composed of two or more columns. A 1NF table with a single column primary key is automatically in at least 2NF. A second normal form (2NF) is a table that is already in 1NF and in which the values in each non-primary-key column can be worked out from the values in all the columns that makes up the primary key.A table in 1NF can be converted into 2NF by removing the columns that can be worked out from only part of the primary key. These columns are placed in a new table along with a copy of the part of the primary key that they can be worked out from. 8. 6Describe the characteristics of a table in second normal form (2NF). Second normal form (2NF) is a table that is already in 1NF and in which the values in each non-primary-key column can only be worked out from the values in all the columns that make up the primary key. 8. Describe what is meant by full functional habituation and describe how this type of dependency relates to 2NF. Provide an example to illustrate your answer. The formal definition of second normal form (2NF) is a table that is in first normal form and every non-primary-key column is fully functionally dependent on the primary key. Full functional dependency indicates that if A and B are columns of a table, B is fully functionally dependent on A, if B is not dependent on any subset of A. If B is dependent on a subset of A, this is referred to as a partial dependency.If a partial dependency exists on the primary key, the table is not in 2NF. The partial dependency must be removed for a table to achieve 2NF. See Section 8. 4 for an example. 8. 8Describe the characteristics of a table in third normal form (3NF). Third normal form (3NF) is a table that is already in 1NF and 2NF, and in which the values in all non-primary-key columns can be worked out from only the primary key (or candidate key) column(s) and no other columns. 8. 9Describe what is meant b y transitive dependency and describe how this type of dependency relates to 3NF. Provide an example to illustrate your answer.The formal definition for third normal form (3NF) is a table that is in first and second normal forms and in which no non-primary-key column is transitively dependent on the primary key. transitive verb dependency is a type of functional dependency that occurs when a particular type of relationship holds between columns of a table. For example, consider a table with columns A, B, and C. If B is functionally dependent on A (A ? B) and C is functionally dependent on B (B ? C), then C is transitively dependent on A via B (provided that A is not functionally dependent on B or C).If a transitive dependency exists on the primary key, the table is not in 3NF. The transitive dependency must be removed for a table to achieve 3NF. See Section 8. 5 for an example. Chapter 9 Logical Database Design Step 1- Review questions 9. 1Describe the purpose of a design methodolog y. A design methodology is a integrated approach that uses procedures, techniques, tools, and documentation aids to support and facilitate the process of design. 9. 2Describe the main phases involved in database design. Database design is made up of two main phases logical and physical database design.Logical database design is the process of constructing a model of the data used in a company based on a specific data model, but independent of a particular DBMS and other physical considerations. In the logical database design phase we build the logical representation of the database, which includes identification of the important entities and relationships, and then translate this representation to a set of tables. The logical data model is a source of information for the physical design phase, providing the physical database designer with a fomite for making tradeoffs that are very important to the design of an efficient database.Physical database design is the process of producing a description of the implementation of the database on secondary storage it describes the base tables, file organizations, and indexes used to achieve efficient access to the data, and any associated integrity constraints and security restrictions. In the physical database design phase we decide how the logical design is to be physically implemented in the target relational DBMS. This phase allows the designer to make decisions on how the database is to be implemented. Therefore, physical design is tailored to a specific DBMS. . 3Identify important factors in the success of database design. The following are important factors to the success of database design Work interactively with the users as much as possible. Follow a structured methodology throughout the data modeling process. Employ a data-driven approach. Incorporate structural and integrity considerations into the data models. Use normalization and transaction validation techniques in the methodology. Use diagrams to represe nt as much of the data models as possible. Use a database design language (DBDL). Build a data dictionary to tag on the data model diagrams. Be willing to repeat steps. 9. 4Discuss the important role played by users in the process of database design. Users play an essential role in confirming that the logical database design is meeting their requirements. Logical database design is made up of two steps and at the end of each step (Steps 1. 9 and 2. 5) users are required to review the design and provide feedback to the designer. Once the logical database design has been signed off by the users the designer can continue to the physical d