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The Theory and Practice of Information Modelling
Information Systems - Lecture 9
Chris S. Johnson

Ref - Lecture Notes & Chapters 6 RISD Bell & Wood-Harper
Topics

Video - The Career of an Analyst - 25 mins

Review Enitity Relationships

Review the Concept of Keys

Normalisation

Objectives

- understand the importance of continually learning

- appreciate the role of Entity Relationship Diagrams

- appreciate the job of a consultant

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Entity Relationship Model Revisited
Entity Relationships - data at rest - independent of process
Consists of -Entity or nouns (objects) - real or abstract - multiple occurrences (e.g. customers, students, cars) (i.e. instances in OOT) - Relationships between entities are natural associations between one or more entities consider the verb in a sentence

Why are Entity-Relationships Important
- quick to draw (model)
- conceptually simple to understand
- map almost directly to a Relational Database (RDBMS - Relational Database management System)
- provide a bridging step to an Object Oriented Model
- are the basis of all user database software products e.g. MS-ACCESS, Borland's Paradox, DBase 5,
Entity Relationship Model
Hints for Drawing Entity Relationship Diagrams - Identify the entities/nouns - Identify the relations - name with a verb - such that the diagram reads in simple sentences - Identify relations as 1:1, 1:M & M:N - Identifying The Entity Attributes The adjectives describing the entities (covered in The Role of Data) - Identify the KEY attributes The attributes(s) that uniquely identifies the entity - single field and multiple field keys (combination keys) - combination keys that uniquely identify the relationship e.g. Student number & Subject number
Entity Relationship Model
The IMPORTANCE OF KEYS - the basis of the relationship between entities - a key is a logical (and physical) pointer (POINTER