Systems Analysis and Design Allen Dennis and Barbara Haley

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Transcript Systems Analysis and Design Allen Dennis and Barbara Haley

Object Persistence Design

Key Definitions

Object persistence

performance.

involves the selection of a storage format and optimization for Four basic formats used for object persistence are:

files, OO databases, object-relational, and relational databases

OBJECT PERSISTENCE FORMATS

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 Slide 4 PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved.

Other files

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

Customer Order File

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 Slide 7 PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved.

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 Slide 8 PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved.

Relational Database Example

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 Slide 10 PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved.

Selecting an Object Persistence Format

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?

MAPPING PROBLEM DOMAIN OBJECTS TO OBJECT PERSISTENCE FORMATS

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 Slide 14 PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved.

Appointment System Problem Domain and Data Management Layers

Factoring Out Multiple Inheritance Effect

Mapping Problem Domain Objects to ORDBMS Schema -- Rules

Mapping Problem Domain Objects to ORDBMS Schema -- Example

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 Slide 19 PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved.

Mapping Problem Domain Objects to RDBMS Schema -- Rules

OPTIMIZING RDBMS-BASED OBJECT STORAGE

Dimensions of Data Storage Optimization

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

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 Slide 23 PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved.

The Steps of Normalization

First Normal Form (1NF)

Second Normal Form (2NF)

Third Normal Form (3NF)

Optimizing Access Speed

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

Payment Type Index

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 Slide 30 PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved.

Estimating Data Storage Size

Field Average Size (Characters) Order number Date Cust ID Last name First name State Amount Tax rate

Record Size

Overhead (30%)

Total Record Size

8 7 4 13 9 2 4 2

14.7

63.7

Initial Table Size 50,000 Initial Table Volume 3,185,000 Growth/Month Table volume @ 3 years 1,000 5,478,200 Slide 31 PowerPoint Presentation for Dennis, Wixom & Tegardem Systems Analysis and Design Copyright 2001 © John Wiley & Sons, Inc. All rights reserved.

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 speed of access

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