Chapter 09: Database Design Essay 71. List and briefly describe the three types of system maintenance activities. ANSWER: The three types of maintenance activities are: 1. Corrective maintenance in response to systems errors. 2. Adaptive maintenance due to changes in the business environment. 3. Perfective maintenance to enhance the system. DIFFICULTY: REFERENCES: LEARNINGOBJECTIVES: Difficulty: Moderate 9-2e Maintenance 09.02 - Describe the five phases in the Systems Development Life Cycle (SDLC) 72. List and describe the different levels at which database backups can be performed. ANSWER: A full backup, or dump, of the entire database. In this case, all database objects are backed up in their entirety. A differential backup of the database, in which only the objects that have been updated or modified since the last full backup are backed up. A transaction log backup, which backs up only the transaction log operations that are not reflected in a previous backup copy of the database. In this case, no other database objects are backed up. DIFFICULTY: Difficulty: Moderate REFERENCES: 9-3d Testing and Evaluation LEARNINGOBJE 09.03 - Design databases using the six phases in the Database Life Cycle (DBLC) framework CTIVES: 73. What are the factors affecting the purchasing decision for DBMS software? ANSWER: Cost: This includes the original purchase price, along with maintenance, operational, license, installation, training, and conversion costs. DBMS features and tools: Some database software includes a variety of tools that facilitate application development. For example, the availability of query by example (QBE), screen painters, report generators, application generators, and data dictionaries helps to create a more pleasant work environment for both the end user and the application programmer. Database administrator facilities, query facilities, ease of use, performance, security, concurrency control, transaction processing, and third-party support also influence DBMS software selection. Underlying model: This can be hierarchical, network, relational, object/relational, or object-oriented. Portability: A DBMS can be portable across platforms, systems, and languages. DBMS hardware requirements: Items to consider include processor(s), RAM, disk space, and so on. DIFFICULTY: Difficulty: Moderate REFERENCES: 9-5 DBMS Software Selection LEARNINGOBJE 09.03 - Design databases using the six phases in the Database Life Cycle (DBLC) framework CTIVES: Page13 Chapter 09: Database Design 74. Explain the concept of logical design and list the steps involved. ANSWER: Logical design is the second stage in the database design process. The logical design goal is to design an enterprise-wide database that is based on a specific data model but independent of physical-level details. Logical design requires that all objects in the conceptual model be mapped to the specific constructs used by the selected database model. The logical design is generally performed in the following four steps: 1. Mapping the conceptual model to logical model components 2. Validating the logical model using normalization 3. Validating the logical model integrity constraints 4. Validating the logical model against user requirements DIFFICULTY: Difficulty: Moderate REFERENCES: 9-6 Logical Design LEARNINGOBJE 09.03 - Design databases using the six phases in the Database Life Cycle (DBLC) framework CTIVES: 75. Explain the differences between a centralized and decentralized approach to database design. ANSWER: Centralized design is productive when the data component has a relatively small number of objects and procedures. The design can be carried out and represented in a fairly simple database. Centralized design is typical of relatively simple, small databases and can be successfully done by a single database administrator or by a small, informal design team. The company operations and the scope of the problem are sufficiently limited to allow even a single designer to define the problem(s), create the conceptual design, verify the conceptual design with the user views, define system processes and data constraints to ensure the efficacy of the design, and ensure that the design will comply with all the requirements. On the other hand, decentralized design might be used when the system’s data component has a considerable number of entities and complex relations on which very complex operations are performed. Decentralized design is also often used when the problem itself is spread across several operational sites and each element is a subset of the entire data set. In large and complex projects, the database typically cannot be designed by only one person. Instead, a carefully selected team of database designers tackles a complex database project. Within the decentralized design framework, the database design task is divided into several modules. Once the design criteria have been established, the lead designer assigns design subsets or modules to design groups within the team. DIFFICULTY: Difficulty: Moderate REFERENCES: 9-9 Centralized versus Decentralized Design LEARNINGOBJE 09.06 - Distinguish between centralized and decentralized conceptual database design CTIVES: Page14