ICT117 Week11 Data Management s

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PowerPoint Presentation for Dennis, Wixom, & Tegarden Systems Analysis and Design with UML, 3rd Edition Copyright © 2009 John Wiley & Sons, Inc. All rights reserved.

Data Management Layer

Design



17 March, 2011 ICT117 Systems Analysis & Design. Semester 2, 2010.

Includes John Wiley & Sons © material.

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ObjectivesBecome familiar with several object-persistence formats.

Be able to map problem domain objects to different object-persistence formats.

Be able to apply the steps of normalisation to a relational

database.Be able to optimise a relational database for object storage

and access.

Become familiar with indexes for relational databases.

Be able to estimate the size of a relational database.Be able to design the data access and manipulation

classes.





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The Data Management LayerIncludes:

data access and data manipulation logic

the actual design of the storage

Four-step design approach

Select the format of the storage

Map the problem-domain objects to an object-persistence format

optimise the object-persistence format

design the data access and manipulation classes




OBJECT PERSISTENCE

FORMATS





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Object Persistence FormatsFiles (Sequential and Random)

Relational databases

Object-relational databases

Object-oriented databases





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Sample File

Fictitious customer database





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Sequential & Random

Access FilesSequential access files allow sequentialoperations (assumes disc storage)Read, write, and search

Efficient for report writingSearches are not efficient because on average

50% of records have to be accessed

Two versions

Ordered (linked list)Unordered (chronological placement)





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Random Access FilesAllow only random or direct file operations

Good for finding and updating a specific object

Inefficient for report writing

Require a key or index to locate the desiredrecord





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Application File TypesMaster Files

Look-up or Reference files

Transaction files or Journals

Audit file

History file





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Relational DatabasesCollection of tablesA table is comprised of rows of attributes that

define an entity

Each row in the table is a unique record

The same attribute in each record is the primarykey of the table. Each key value must be unique

Tables are related to each otherA foreign key is a record attribute that is the

primary key of another tableRelationships established by linking foreign key of

one table to the primary key of another table





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Database Management

System - DBMS

Software that creates and manipulates adatabase

RDBMS is a DBMS for a relational database

RDBMS usually support Referential Integrity

the idea of ensuring that values linking the tables

together (references) through the primary and

foreign keys are valid and correctly synchronised





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Referential Integrity ExampleThe class Customer has an attribute custID

The class Order has an attribute custID thatindicates the customer who placed the order

You should not be able to:

create an order for a non-existent Customer;

delete a Customer who has existing orders;

change the custID value of a Customer, unless youalso change the custID values of the related

orders (caveat – never change primary keys)





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The Structured Query

Language: SQLA standard language for manipulating data in

tables: DDL and DML

SQL Commands enable the functions:Create, edit, and delete tables

Add, edit, and delete data

Display data from one or more related tables

Display data computed from data in one or morerelated tables

Studied in ICT118 Database and Info Retrieval





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Selecting Persistence Formats




MAPPING PROBLEM-DOMAIN

OBJECTS TO OBJECT-

PERSISTENCE FORMATS





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Mapping PD Classes to RDBMSMap all concrete problem domain classes to the

RDBMS tables.

Map single valued attributes to columns of the tables.

Map methods to stored procedures or to program

modules.

Map single-valued aggregation and associationrelationships to a column that can store the key ofthe related table

Map multi-valued attributes and repeating groups tonew tables and create a one-to-many associationfrom the original table to the new ones.





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Mapping PD Classes to RDBMSMap multi-valued aggregation and association relationships

to a new associative table that relates the two originaltables together. Copy the primary key from both originaltables to the new associative table

For aggregation and association relationships of mixedtype, copy the primary key from the single-valued side(1..1 or 0..1) of the relationship to a new column in thetable on the multi-valued side (1..* or 0..*) of therelationship that can store the key of the related table

Ensure that the primary key of the subclass instance is thesame as the primary key of the superclass..




OPTIMISING RDBMS-BASED

OBJECT STORAGE





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Optimising Storage EfficiencyNo redundant data:

Wastes space – an issue in large scaleinformation system

Allows more opportunities for error

Few null values in tables:

Null is difficult to interpret





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Normalisation

Tells us how well-formed the data is in anRDBMS

Reduces data redundancies

First four levels of normalisation are

1 Normal Form: removes multi-valued fields

2 Normal Form: removes partial-key dependencies

3 Normal Form: removes transitive dependencies(dependence on non-primary key fields)

Boyce-Codd Normal Form: every determinant is a

candidate key





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Steps of Normalisation





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Next lecture

HCI – Human Computer Interface design

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