Conceptual and Logical Design

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1 Conceptual and Logical Design Lecture 3 (Part 1) Akhtar Ali

2 Building Conceptual Data Model To build a conceptual data model of the data requirements of the enterprise. Model comprises entity types, relationship types, attributes and attribute domains, primary and alternate keys, and integrity constraints. Step 1 Identify entity types To identify the required entity types. Step 2 Identify relationship types To identify the important relationships that exist between the entity types. 2 Pearson Education 2009

3 Building Conceptual Data Model... Step 3 Identify and associate attributes with entity or relationship types To associate attributes with the appropriate entity or relationship types and document the details of each attribute. Step 4 Determine attribute domains To determine domains for the attributes in the data model and document the details of each domain. 3 Pearson Education 2009

4 Building Conceptual Data Model... Step 5 Determine candidate, primary, and alternate key attributes To identify the candidate key(s) for each entity and if there is more than one candidate key, to choose one to be the primary key and the others as alternate keys. Step 6 Consider use of enhanced modeling concepts (optional step) To consider the use of enhanced modeling concepts, such as specialization / generalization, aggregation, and composition. We will cover this topic at a later stage. 4 Pearson Education 2009

5 Step 1 Identify entity types Examine the requirements specifications text Identify noun and noun phrases (e.g., student) A common / improper noun implies an entity type (e.g., country) A proper noun implies an instance of an entity type (e.g., UK) Look for major objects (e.g., people, places, things, etc) Look for objects that have an existence in their own right (e.g., Staff is an entity because staff exist in the enterprise.) Look for multiple objects rather than singular ones (e.g., Video is an entity type in the DVD rental company but Company is not an entity in this scenario as we are not talking about multiple instances / companies).

6 Step 2 Identify relationship types A transitive verb implies a relationship type. A transitive verb needs an object to complete the meaning of the sentence, e.g., in a student may borrow many books, borrow is a transitive verb and implies a relationship between student and book entity types. A having verb implies a relationship type. Verbs or verb phrases that signifies possession, e.g., staff owns a car, department has staff.

7 Step 3 Identify and associate attributes with entity or relationship types An adjective implies an attribute of an entity type. An adjective is a word that tells us more about a noun (e.g., colour, size, time). An adverb implies an attribute of a relationship type. An adverb is a word that tells us more about a verb. An adverb "qualifies" or "modifies" a verb (The man ran quickly). But adverbs can also modify adjectives (Tara is really beautiful), or even other adverbs (It works very well). An intransitive verb may identify an attribute. An intransitive verb is one which does not need any object or element to complete the meaning, e.g., the train arrives every morning at 7:30 am. Here arrives is an intransitive verb and points to the arrival time attribute. A noun phrase which follows identified by may indicate an attribute, e.g., a person is identified by person id and surname. Attributes can be identified where the noun or noun phrase is a property, quality, identifier or characteristic of an entity or relationship type. If X is an entity type, asking what information are we required to hold on X may help identify the attributes.

8 Conceptual (ERD) Logical Mapping (Relations)

9 ER diagram of Staff user view of DreamHome

10 Relations for the Staff user views of DreamHome

Data Analysis 1. Chapter 2.1 V3.1. Napier University Dr Gordon Russell

Data Analysis 1. Chapter 2.1 V3.1. Napier University Dr Gordon Russell Data Analysis 1 Chapter 2.1 V3.1 Copyright @ Napier University Dr Gordon Russell Entity Relationship Modelling Overview Database Analysis Life Cycle Components of an Entity Relationship Diagram What is