Lecture 09 dblc centralized vs decentralized design
- 1. Lecture 9 Database Design DBLC and Centralized vs Decentralize Design
- 2. Data Raw facts stored in databases Need additional processing to become useful Information Required by decision maker Data processed and presented in a meaningful form Transformation Changing Data into Information
- 3. Database Carefully designed and constructed repository of facts Part of an information system Information System Provides data collection, storage, and retrieval Facilitates data transformation Components include: People Hardware Software The Information System Database(s) Application programs Procedures
- 4. System Analysis Establishes need and extent of an information system Systems development Process of creating information system Database development Process of database design and implementation Creation of database models Implementation Creating storage structure Loading data into database Providing for data management The Information System (Con’t.)
- 5. Systems Development Life Cycle Figure 6.2
- 6. Database Lifecycle (DBLC) Figure 6.3
- 7. Phase 1: Database Initial Study Purposes Analyze company situation Operating environment Organizational structure Define problems and constraints Define objectives Define scope and boundaries
- 8. Initial Study Activities Figure 6.4
- 9. Phase 2: Database Design Most Critical DBLC phase Makes sure final product meets requirements Focus on data requirements Subphases Create conceptual design DBMS software selection Create logical design Create physical design
- 10. Two Views of Data Figure 6.5
- 11. I. Conceptual Design Data modeling creates abstract data structure to represent real-world items High level of abstraction Four steps Data analysis and requirements Entity relationship modeling and normalization Data model verification Distributed database design
- 12. Data analysis and Requirements Focus on: Information needs Information users Information sources Information constitution Data sources Developing and gathering end-user data views Direct observation of current system Interfacing with systems design group Business rules
- 13. Entity Relationship Modeling and Normalization Table 6.2
- 14. E-R Modeling is Iterative Figure 6.8
- 15. Concept Design: Tools and Sources Figure 6.9
- 16. Data Model Verification E-R model is verified against proposed system processes End user views and required transactions Access paths, security, concurrency control Business-imposed data requirements and constraints Reveals additional entity and attribute details Define major components as modules Cohesivity Coupling
- 17. E-R Model Verification Process Table 6.4
- 18. Iterative Process of Verification Figure 6.10
- 19. Distributed Database Design Design portions in different physical locations Development of data distribution and allocation strategies
- 20. II. DBMS Software Selection DBMS software selection is critical Advantages and disadvantages need study Factors affecting purchasing decision Cost DBMS features and tools Underlying model Portability DBMS hardware requirements
- 21. III. Logical Design Translates conceptual design into internal model Maps objects in model to specific DBMS constructs Design components Tables Indexes Views Transactions Access authorities Others
- 22. IV. Physical Design Selection of data storage and access characteristics Very technical More important in older hierarchical and network models Becomes more complex for distributed systems Designers favor software that hides physical details
- 23. Physical Organization Figure 6.12
- 24. Phase 3: Implementation and Loading Creation of special storage-related constructs to house end-user tables Data loaded into tables Other issues Performance Security Backup and recovery Integrity Company standards Concurrency controls
- 25. Phase 4: Testing and Evaluation Database is tested and fine-tuned for performance, integrity, concurrent access, and security constraints Done in parallel with application programming Actions taken if tests fail Fine-tuning based on reference manuals Modification of physical design Modification of logical design Upgrade or change DBMS software or hardware
- 26. Phase 5: Operation Database considered operational Starts process of system evaluation Unforeseen problems may surface Demand for change is constant
- 27. Phase 6: Maintenance and Evaluation Preventative maintenance Corrective maintenance Adaptive maintenance Assignment of access permissions Generation of database access statistics to monitor performance Periodic security audits based on system-generated statistics Periodic system usage-summaries
- 28. DB Design Strategy Notes Top-down 1) Identify data sets 2) Define data elements Bottom-up 1) Identify data elements 2) Group them into data sets
- 29. Top-Down vs. Bottom-Up Figure 6.14
- 30. Centralized vs. Decentralized Design Centralized design Typical of simple databases Conducted by single person or small team Decentralized design Larger numbers of entities and complex relations Spread across multiple sites Developed by teams
- 32. Decentralized Design Figure 6.16
- 33. Centralized vs. Decentralized Design (continued) Aggregation process Requires designer to create single model in which various aggregation problems must be addressed: Synonyms and homonyms Entity and entity subtypes Conflicting object definitions
- 34. Centralized vs. Decentralized Design (continued)