Introduction to Data Analysis and Logic Specification Objectives

Introduction to Data Analysis and Logic Specification Objectives l Draw an entity-relationship diagram, and explain the types of entity relationships l Define cardinality, cardinality notation, and crow’s foot notation l Demonstrate the use of structured English, decision tables, and decision trees to develop information system process descriptions l Explain the relationships among data flow Lecture 9 diagrams, the data dictionary, and process 1

Data Analysis - Introduction Data terminology and concepts l Relationships among data objects l Entity-relationship diagrams (ERDs) l Lecture 9 2

Data Terminology and Concepts l Data design includes – – – Lecture 9 Entities Fields Records Files Keys 3

Data Terminology and Concepts l Definition – Entity: a person, place, thing, or event for which data is collected and maintained – Entity-relationship diagrams (ERDs): an ERD is a graphical model that shows relationships among system entities Lecture 9 4

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Data Relationships and Entity. Relationship Diagrams l Entity-relationship diagrams (ERDs) – Each entity is a rectangle, labeled with a noun – Each relationship is a diamond, labeled with a verb – Types of relationships One-to-one (1: 1) l One-to-many (1: M) l Many-to-many (M: N) l – A full ERD shows all system relationships Lecture 9 6

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Data Relationships and Entity. Relationship Diagrams l One-to-one (1: 1) relationship – Exists when exactly one of the second entity occurs for each instance of the first entity – Examples One office manager heads one office l One vehicle ID number is assigned to one vehicle l One driver drives one delivery truck l One faculty member is chairperson of one department l Lecture 9 8

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Data Relationships and Entity. Relationship Diagrams l One-to-many (1: M) relationship – Exists when one occurrence of the first entity can be related to many occurrences of the second entity, but each occurrence of the second entity can be associated with only one occurrence of the first entity – Examples One individual owns many automobiles l One customer places many orders l One department employs many employees l One faculty advisor advises many students l Lecture 9 10

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Data Relationships and Entity. Relationship Diagrams l Many-to-many (M: N) relationship – Exists when one instance of the first entity can be related to many instances of the second entity, and one instance of the second entity can be related to many instances of the first – Examples A student enrolls in one or more classes, and each class has one or more students registered l A passenger buys tickets for one or more flights, and each flight has one or more passengers l An order lists one or more products, and each product is listed on one or more orders l Lecture 9 12

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Data Relationships and Entity. Relationship Diagrams l A full ERD shows all system relationships – Examples A sales rep serves one or more customers, but each customer has only one sales rep l A customer places one or more orders, but each order has only one customer l An order lists one or more products, and each product can be listed in one or more orders l A warehouse stores one or more products, and each product can be stored in one or more warehouses l Lecture 9 14

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Data Relationships and Entity. Relationship Diagrams l Cardinality – Describes how instances of one entity relate to another – Mandatory vs. optional relationships – Crow’s foot notation is one method of showing cardinality – Most CASE products support the drawing of ERDs Lecture 9 16

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Data Relationships and Entity. Relationship Diagrams l Creating an ERD 1. Identify the entities 2. Determine all significant events or activities for two or more entities 3. Analyze the nature of the interaction 4. Draw the ERD Lecture 9 18

Process Description Tools l Structured English – Subset of standard English – Describes process logic Use only standard sequence, selection, and iteration structures l Use indentation for readability l Use a limited vocabulary l Lecture 9 19

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Process Description Tools l Decision tables – Show a logical structure that describes process logic – Every logical combination is shown initially – Results then can be combined and simplified – Programmers can use decision tables in developing code Lecture 9 21

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Process Description Tools l Lecture 9 Decision tables 23

Process Description Tools l Steps of constructing a Decision tables – Step 1. Analyze the procedure l Identity conditions and actions – Step 2. Calculate the number of rules l number of rules = 2 n where n = the number of conditions – Step 3. Evaluate the number of outcomes l Lecture 9 Analyze the combination of condition to see what outcome should be undertaken – Step 4. Draw up the decision table 24

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Process Description Tools l Decision trees – Graphical representation that shows a decision table’s conditions, actions, and rules – Logic structure is shown horizontally – Easy to construct and understand – Decision table is better in complex situations Lecture 9 27

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