Object Persistence Design

1. Object Persistence Design Chapter 13

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. OBJECT PERSISTENCE FORMATS

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. Other files • Master files • Transaction files • Audit • History • Look-up

6. Customer Order File Figure 13-1 Goes Here

7. 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 Relational Databases

8. Relational databases extended to handle the storage of objects Use of user-defined data types Extended SQL Inheritance tends to be language dependent Object-Relational Databases

9. Relational Database Example Figure 13-3 Goes Here

10. 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 Object-Oriented Databases

11. Selecting an Object Persistence Format

12. MAPPING PROBLEM DOMAIN OBJECTS TO OBJECT PERSISTENCE FORMATS

13. Initial Points to Consider • Adding primary and foreign keys • Unless they add too much overhead • Data management functionality only in classes at datamanagement layer • May add overhead, but aids in portability and reuse

14. Appointment System Problem Domain and Data Management Layers

15. Factoring Out Multiple Inheritance Effect

16. Mapping Problem Domain Objects to ORDBMS Schema -- Rules

17. Mapping Problem Domain Objects to ORDBMS Schema -- Example

18. 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 Maintain a Clean Problem Domain Layer

19. Mapping Problem Domain Objects to RDBMS Schema -- Rules

20. OPTIMIZING RDBMS-BASED OBJECT STORAGE

21. Dimensions of Data Storage Optimization • Storage efficiency (minimizing storage space) • Speed of access (minimizing time to retrieve desired information)

22. 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

23. The Steps of Normalization

24. First Normal Form (1NF)

25. Second Normal Form (2NF)

26. Third Normal Form (3NF)

27. Denormalization Clustering Intra-file Inter-file Indexing Optimizing Access Speed

28. Payment Type Index

29. 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

30. Estimating Data Storage Size Field Average Size (Characters) Order number 8 Date 7 Cust ID 4 Last name 13 First name 9 State 2 Amount 4 Tax rate 2 Record Size 49 Overhead (30%) 14.7 Total Record Size 63.7 Initial Table Size 50,000 Initial Table Volume 3,185,000 Growth/Month 1,000 Table volume @ 3 years 5,478,200

31. 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.