Object Persistence Design Chapter 13

1
Object Persistence Design Chapter 13

• Alan Dennis, Barbara Wixom, and David Tegarden
• John Wiley Sons, Inc.
• Slides by Fred Niederman
• Edited by Solomon Negash

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 files 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
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
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
Relational Database Example
Figure 13-3 Goes Here
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
Selecting an Object Persistence Format
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
MAPPING PROBLEM DOMAIN OBJECTS TO OBJECT
PERSISTENCE FORMATS

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
Appointment System Problem Domain and Data
Management Layers
16
Factoring Out Multiple Inheritance Effect
17
Mapping Problem Domain Objects to ORDBMS Schema
-- Rules
18
Mapping Problem Domain Objects to ORDBMS Schema
-- Example
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
Mapping Problem Domain Objects to RDBMS Schema --
Rules
21
OPTIMIZING RDBMS-BASED OBJECT STORAGE

22
Dimensions of Data Storage Optimization

• Storage efficiency (minimizing storage space)
• Speed of access (minimizing time to retrieve
  desired information)

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
The Steps of Normalization
25
First Normal Form (1NF)
26
Second Normal Form (2NF)
27
Third Normal Form (3NF)
28
Optimizing Access Speed

• Denormalization
• Clustering
• Intra-file
• Inter-file
• Indexing

29
Payment Type Index
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
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
_at_ 3 years 5,478,200
32
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.