1. PowerPoint Presentation for Dennis, Wixom & Tegarden Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 1 Object Persistence Design Chapter 13

2. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 2 Key Definitions Object persistence involves the selection of a storage format and optimization for performance. Four basic formats used for object persistence are: files, OO databases, object-relational, and relational databases.

3. PowerPoint Presentation for Dennis, Wixom & Tegarden Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 3 OBJECT PERSISTENCE FORMATS

4. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 4 Files Sequential Access Data stored in order based on a particular attribute Typically efficient for reports using all or most of the file’s data Random Access Data stored in unordered fashion Typically efficient for finding individual records

5. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 5 Other files Master files Transaction files Audit History Look-up

6. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 6 Customer Order File Figure 13-1 Goes Here

7. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 7 Relational Databases Primary key Foreign key Referential integrity Structured Query Language (SQL) Tables Joining tables Objects must be converted so they can be stored in a table

8. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 8 Object-Relational Databases Relational databases extended to handle the storage of objects Use of user-defined data types Extended SQL Inheritance tends to be language dependent

9. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 9 Relational Database Example Figure 13-3 Goes Here

10. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 10 Object-Oriented Databases Two approaches Adding persistence extensions to OO languages Separate database management systems  Extents  Object ID assigned  Some inheritance  Repeating groups or multivalued attributes  Mainly support multimedia applications  Sharp learning curve

11. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 11 Selecting an Object Persistence Format

12. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 12 Your Turn A major university graduates about 10,000 students a year and the development office wants to build a web-based system to solicit and track donations. What are the pros and cons of each data storage format for this sort of application?

13. PowerPoint Presentation for Dennis, Wixom & Tegarden Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 13 MAPPING PROBLEM DOMAIN OBJECTS TO OBJECT PERSISTENCE FORMATS

14. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 14 Initial Points to Consider Adding primary and foreign keys Unless they add too much overhead Data management functionality only in classes at data management layer May add overhead, but aids in portability and reuse

15. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 15 Appointment System Problem Domain and Data Management Layers

16. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 16 Factoring Out Multiple Inheritance Effect

17. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 17 Mapping Problem Domain Objects to ORDBMS Schema -- Rules

18. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 18 Mapping Problem Domain Objects to ORDBMS Schema -- Example

19. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 19 Maintain a Clean Problem Domain Layer Modifying the problem domain layer can create problems between the system architecture and human computer interface layer The development and production costs of OODBMS may offset the production cost of having the data management layer implemented in ORDBMS

20. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 20 Mapping Problem Domain Objects to RDBMS Schema -- Rules

21. PowerPoint Presentation for Dennis, Wixom & Tegarden Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 21 OPTIMIZING RDBMS-BASED OBJECT STORAGE

22. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 22 Dimensions of Data Storage Optimization Storage efficiency (minimizing storage space) Speed of access (minimizing time to retrieve desired information)

23. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 23 Optimizing Storage Efficiency Reduce redundant data Limit null values Multiple possible interpretations can lead to mistakes A well-formed logical data model does not contain redundancy or many null values

24. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 24 The Steps of Normalization

25. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 25 First Normal Form (1NF)

26. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 26 Second Normal Form (2NF)

27. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 27 Third Normal Form (3NF)

28. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 28 Optimizing Access Speed Denormalization Clustering Intra-file Inter-file Indexing

29. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 29 Payment Type Index

30. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 30 Guidelines for Creating Indexes Use indexes sparingly for transaction systems Use many indexes to increase response times in decision support systems For each table Create a unique index based on the primary key Create an index based on the foreign key Create an index for fields used frequently for grouping, sorting, or criteria

31. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 31 Estimating Data Storage Size FieldAverage Size (Characters) Order number 8 Date 7 Cust ID 4 Last name13 First name 9 State 2 Amount 4 Tax rate 2 Record Size49 Overhead (30%)14.7 Total Record Size63.7 Initial Table Size50,000 Initial Table Volume 3,185,000 Growth/Month 1,000 Table volume @ 3 years 5,478,200

32. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved.

33. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved.

34. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 34 Summary There are four basic types of object persistence formats: files (sequential and random access), object-oriented databases, object-relational databases, and relational databases. Tradeoffs between the formats make it necessary to consider which to apply in each environment Once the format has been selected, data storage needs to be optimized for efficiency and speed of access.

35. PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved. Slide 35 Expanding the Domain The Object Data Management Group is working on standardization of the OO database features. Check them out at: http://www.odmg.org