La Guerra de los Dos Pedros y sus consecuencias diplomáticas.

1. A user view is the view of data that is necessary to support the operations of a particular user. By considering individual user views instead of the complete design problem, the database design process is greatly simplified.

3. If the design problem were extremely simple, the overall design might not have to be broken down into a consideration of individual user views.

5. The primary key is the column or columns that uniquely identify a given row and that furnish the main mechanism for directly accessing a row in the table. An alternate key is a column or combi- nation of columns that could have functioned as the primary key but was not chosen to do so. A secondary key is a column or combination of columns that is not any other type of key but is of interest for purposes of retrieval. A foreign key is a column or combination of columns in one table whose values are required to match the primary key in another table. Foreign keys furnish the mechanism through which relationships are made explicit.

7. Department (DepartmentNum, DepartmentName)

Advisor (AdvisorNum, LastName, FirstName, DepartmentNum) FK DepartmentNum ! Department

Course (CourseCode, Description)

Student (StudentNum, LastName, FirstName, AdvisorNum) FK AdvisorNum ! Advisor

StudentCourse (StudentNum, CourseCode, Grade) FK StudentNum ! Student

FK CourseCode ! Course 9. a. No change is necessary.

b. Store both the AdvisorNum and DepartmentNum columns in the Student table.

11. The method presented in this text is bottom up; that is, an approach in which specific user requirements are synthesized into a design. By initially reviewing the requirements and determin- ing a possible list of entities prior to following the steps in this method, you can gain the advan- tages to both top-down and bottom-up approaches.

13. Many answers are possible. Be sure the functional dependencies you represent are based on rea-

15. a. There is a many-to-many-to-many relationship between students, courses, and faculty members.

b. There is a many-to-many relationship between students and courses. A faculty number func- tionally determines a course number; that is, each faculty member is associated with exactly one course.

c. There are separate many-to-many relationships between students and courses, courses and faculty members, and students and faculty members.

d. There is a many-to-many relationship between students and courses. A given student number-course number combination uniquely determines a faculty number. That is, when a student takes a course, a single faculty member teaches the course.

e. There is a many-to-many relationship between students and courses. There is also a many- to-many relationship between courses and faculty members. A student number functionally determines a faculty number; that is, each student is associated with exactly one faculty member.

17. If one 3NF relation contains a column that is a determinant for a column in another 3NF relation with the same primary key, merging the relations will produce a relation that is not in third nor- mal form. The following is an example of two such relations:

Student1 (StudentNum, LastName, FirstName, AdvisorNum)

Student2 (StudentNum, LastName, FirstName, AdvisorLast, AdvisorFirst) The following is the result of merging the Student1 and Student2 relations:

Student (StudentNum, LastName, FirstName, AdvisorNum, AdvisorLast, AdvisorFirst) This table is not in third normal form because:

AdvisorNum ! AdvisorLast, AdvisorFirst

CHAPTER 7—DBMS FUNCTIONS

1. In updating and retrieving data, users do not need to know how data is physically structured on disk nor what processes the DBMS uses to manipulate the data. These structures and manipula- tions are solely the responsibility of the DBMS.

3. Most PC-based DBMSs contain a catalog that maintains metadata about tables, fields, table rela- tionships, views, indexes, users, privileges, and replicated data. Large, expensive DBMSs usually contain a data dictionary that serves as a super-catalog containing the same metadata as a catalog and additional metadata such as that needed to track fragmented data.

5. A lost update could occur in a concurrent update situation when two users attempt to update the same data at the same time, and the DBMS does not have concurrency update features such as two-phase locking or timestamping.

7. A transaction is a set of steps completed by a DBMS that accomplishes a single user task; the DBMS must successfully complete all transaction steps or none at all for the database to remain in a correct state.

9. Deadlock occurs in a concurrent update situation when the first user is waiting for data that has been locked by a second user, and the second user is waiting for data that has been locked by the first user. Unless outside action occurs, each user could wait for the other’s data forever. Deadlock occurs when each of the two users is attempting to access data that is locked by the other user.

11. Recovery is the process of returning the database to a state that is known to be correct from a state known to be incorrect.

13. A DBA uses forward recovery when a catastrophe destroys a database. Forward recovery consists of two steps. First, the DBA copies the most recent database backup over the live database. Second, the DBMS forward recovery feature uses the log to apply after images for committed transactions.

15. Security is the prevention of unauthorized access, either intentional or accidental, to a database. 17. Authentication refers to techniques for identifying the person who is attempting to access the

DBMS. Three types of authentication are passwords, biometrics, and database passwords. A pass- word is a string of characters assigned by the DBA to a user that the user must enter to access to the database. Biometrics identify users by physical characteristics such as fingerprints, voice- prints, handwritten signatures, and facial characteristics. A database password is a string of char- acters assigned by the DBA to a database that users must enter before they can access the database.

19. Permissions specify what kind of access a user has to objects in a database. A workgroup is a group of users, and a DBA usually assigns appropriate permissions to workgroups.

21. Privacy refers to the right of individuals to have certain information about them kept confidential. Privacy and security are related because it is only through appropriate security measures that privacy can be ensured.

23. Data independence is a property that lets you change a database structure without requiring you to change the programs that access the database.

25. Some utility services that a DBMS should provide include: services that let you change the data- base structure; services that let you add new indexes and delete indexes that are no longer needed; facilities that let you use the services available from your operating system; services that let you export data to and import data from other software products; services that provide support for easy-to-use edit and query capabilities, screen generators, report generators, and so on; support for both procedural and nonprocedural languages; and support for an easy-to-use

menu-driven or switchboard-driven interface that allows users to tap into the power of the DBMS without having to resort to a complicated set of commands.

CHAPTER 8—DATABASE ADMINISTRATION

1. The DBA is the database administrator, or the person responsible for the database. The DBA is necessary because his responsibilities are critical to success in a database environment, especially when the database is shared among many users.

3. After the DBA determines the access privileges for each user, the DBA creates security policies and procedures, obtains management approval of the policies and procedures, and then distri- butes them to authorized users. The DBA uses the DBMS’s security features, such as encryption, authentication, authorizations, and views, and also uses special security programs, if necessary. Finally, the DBA monitors database usage to detect potential security violations and takes correc- tive action if a violation occurs.

5. Certain data, although no longer needed in the production database, must be kept for future refer- ence. A data archive is a place for storing this type of data. The use of data archives lets an organiza- tion keep data indefinitely, without causing the database to become unnecessarily large. Data can be removed from the database and placed in the data archive, instead of just being deleted.

7. A shared lock permits other users to read the data. An exclusive lock prevents other users from accessing the data in any way.

9. Context-sensitive help means that if a user is having trouble and asks for help, the DBMS will provide assistance for the particular feature being used at the time the user asks for help. 11. The DBA installs the DBMS, makes any changes to its configuration when they are required,

determines whether it is appropriate to install a new version of the DBMS when it becomes avail- able, applies any vendor fixes to problems, coordinates problem resolution, and coordinates the

CHAPTER 9—DATABASE MANAGEMENT APPROACHES

1. A distributed database is a single logical database that is physically divided among computers at several sites on a network. A distributed database management system (DDBMS) is a DBMS capa- ble of supporting and manipulating distributed databases.

3. A homogeneous DDDBS is one that has the same local DBMS at each site. A heterogeneous DDBMS is one that does not; there are at least two sites at which the local DBMSs are different. Heterogeneous systems are more complex.

5. Location transparency is the characteristic of a DDBMS that states that users do not need to be aware of the location of data in a distributed database. Data should be accessible at a remote site just as easily as it is at a local site; the only difference should be the response time.

7. Replication transparency is the characteristic that users do not need to be aware of any replica- tion that has taken place in a distributed database. The DDBMS should handle updates to all copies of the data without users being aware of the steps taken by the DDBMS.

9. Fragmentation transparency is the characteristic that users do not need to be aware of any data fragmentation (splitting of data) in a distributed database. Users should feel as if they are using a single central database, even if data is stored at different sites.

11. In a well-designed distributed database, you can often increase its capacity by increasing the capacity at only one site. Also, you can increase capacity through the addition of new sites to the network.

13. Increased efficiency is an advantage in a distributed database because data available locally can be retrieved much more rapidly than data stored on a remote, centralized system.

15. Query processing is more complex in a distributed environment because of the difference between the time it takes to send messages between sites and the time it takes to access a disk. 17. With a two-phase commit, one site (often the site initiating the update) acts as coordinator. In the

first phase, the coordinator sends messages to all other sites requesting they prepare to update the database (or acquire all necessary locks). Once the coordinator receives positive replies from all sites, the coordinator sends a message to each site to commit the update. At this point, each site must proceed with the commit process, and all sites must abort if any reply is negative. Two- phase commit guarantees consistency of the database.

19. The information-level design process is unaffected by the fact that the database is distributed. 21. The 12 rules against which you can measure DDBMSs are:

• Local autonomy: No site should depend on another site to perform its functions.

• No reliance on a central site: A DDBMS should not need to rely on one site more than any other site.

• Continuous operation: Performing any function should not shut down the entire distributed database.

• Location transparency: Users should feel as if the entire database is stored at their location. • Fragmentation transparency: Users should feel as if they are using a single central database. • Replication transparency: Users should not be aware of any data replication.

• Distributed query processing: A DDBMS must process queries as rapidly as possible even though the data is distributed.

• Distributed transaction management: A DDBMS must effectively manage transaction updates at multiple sites.

• Hardware independence: A DDBMS must be able to run on different types of hardware. • Operating system independence: A DDBMS must be able to run on different operating

systems.

• Network independence: A DDBMS must be able to run on different types of networks. • DBMS independence: A DDBMS must be heterogeneous.

23. Placing the business functions on the client causes a client maintenance problem. Whenever pro- grammers change the business functions, they must place the updated business functions on every client. Placing the business functions on the server causes a scalability problem and might cause the server to become a bottleneck and degrade the system’s responsiveness to clients. 25. Scalability is the ability of a computer system to continue to function well even as utilization of

the system increases.

27. Compared to a file server, the advantages of a client/server architecture are: lower network traffic; improved processing distribution; thinner clients; greater processing transparency; increased net- work, hardware, and software transparency; improved security; decreased costs; and increased scalability.

29. Dynamic Web pages are Web pages whose content changes in response to the different inputs and choices made by Web clients. You can use client-side extensions embedded in HTML documents or contained in separate files, or you can use server-side extensions usually contained in sepa- rately executed programs.

31. XML (Extensible Markup Language) is a metalanguage derived from a restricted subset of SGML and is designed for the exchange of data on the Web. Using XML, you can create text documents that follow simple, specific rules for their content, and you can define new tags that define the data in the document and the structure of the data, so that programs running on any platform can interpret and process the document.

33. XSL Transformations (XSLT) define the rules to process an XML document and change it into another document; this other document could be another XML document, an XSL document, an HTML or XHTML document, or most any other type of document.

35. A data warehouse is a subject-oriented, time-variant, nonvolatile collection of data in support of management’s decision-making process.

37. A fact table in a data warehouse consists of rows that contain consolidated and summarized data. 39. Using OLAP software, users slice and dice data, drill down data, and roll up data.

41. You can measure OLAP systems against the following 12 rules: users should be able to view data in a multidimensional way; users should not have to know they are using a multidimensional database; users should perceive data as a single user view; the size and complexity of the ware- house should not affect reporting performance; the server portion of the OLAP software should allow the use of different types of clients; each data dimension should have the same structural and operational capabilities; missing data should be handled correctly and efficiently; OLAP should provide secure, concurrent access; users should be able to perform the same operations across any number of dimensions; users should not need to use special interfaces to make their requests; users should be able to report data results any way they want; and OLAP software should allow at least 15 data dimensions and an unlimited number of summary levels. 43. A domain is the set of values that are permitted for an attribute.

45. A method is an action defined for an object. A message is a request to execute a method. To exe- cute the steps in a method, you must send a message to the object.

47. The Unified Modeling Language (UML) is an approach you can use to model the various aspects of software development for object-oriented systems.

49. A visibility symbol in UML indicates whether other classes can view or update the value in an attribute in a class.

51. Generalization is the relationship between a superclass and a subclass.

A P P E N D I X

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