Object Persistence (Data Base) Design Chapter 13

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, and relational databases.

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

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

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 Repeating groups or multivalued attributes

Object-Oriented Databases Two approaches –Adding persistence extensions to OO languages –Separate database management systems Extents (tables) Object ID assigned Some inheritance Repeating groups or multivalued attributes Sharp learning curve

MAPPING PROBLEM DOMAIN OBJECTS TO OBJECT PERSISTENCE FORMATS

Mapping Problem Domain Objects to RDBMS Schema -- Rules

OPTIMIZING RDBMS-BASED OBJECT STORAGE

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

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

The Steps of Normalization

Optimizing Access Speed Denormalization Clustering –Intra-file –Inter-file Indexing

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

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 3 years 5,478,200