3.0 CONCEPTUAL DESIGN

3.0 CONCEPTUAL DESIGN

1. 3.1 ER Modelling

   • Business Rules
     • Definition
       • A business rules is a brief, precise, and unambiguous description of a policy, procedure, or principle within a specific organization
     • Business rules derived from a detailed description of an organizations operations help to create and enforce actions within that organizations environment
     • Properly written business rules are used to define entities, attributes, relationships, and constraints
     • Any time you see relationship statements such as "an agent can serve many customers and each customer can be served by only one agent,"business rules at a work
     • Business rules must be easy to understand and widely disseminated to ensure that every person in the organization shares a common interpretation of the rules
     • Business rules describe, in simple language, the main and distinguishing characteristics of the data as viewed by the company
     • Example
       • A customer may generate many invoices
       • An invoice is generated by only one customer
       • A training session cannot be scheduled for fewer than 10 employees or for more than 30 employees
     • Why Business Rules?
       • It helps to standardize the company's view of data
       • It can be a communication tool between users and designers
       • It allows the designer to understand the nature, role, and scope of the data
       • It allows the designer to understand business processes
       • It allows the designer to develop appropriate relationship participation rules and constraints and to create an accurate data model
     • Translating Business Rules into Data Model Components
       • As a general rule, a noun in business rule will translate into an entity in the model, and a verb(active or passive) that associates the nouns will translate into a relationship among the entities
       • For example, the business rule" a customer may generate many issues" contains two nouns (customer and invoices) and a verb (generate) that associates the nouns
       • From this business rule, you could deduce the following:
         • Customer and invoice are objects of interest for the environment and should be represented by their respective entites
         • There is generate relationship between customer and invoice
       • To properly identify the type of relationship, you should consider that relationships are bidirectional that is they go both ways
       • For example, the business rule " a customer may generate many invoices" is complemented by the business rule "an invoice is generated by only one customer"
         • In that case, the relationship is one-to-many (1:M)
         • Customer is the "I" side, and invoice is the "many" side
       • Generally, to properly identify the relationship type you should ask two questions
         • How many instances of B are related to one instances of A?
         • How many instances of A are related to one instances of B?
       • Example 1
         • You access the relationship between student and class by asking two questions:
           • In how many classes can one student enroll?
             • many classes
           • How many students can enroll in one class?
             • many students
       • Example 2
         • You can access the relationship between employee and company for by asking two questions
           • How many company cars can one company car be assigned?
             • one company car
           • How many employees can be one company car be assigned to?
             • one employee
           • The relational between employee and company car is one-to-one(1:1)
     • Summary
       • Business rules can be translated into data model components based on the following rules:
         • Nouns translate into entites
         • Verbs translate into relationships among entities
         • relationships are bidirectional
   • Relationship and Connectivity
     • Definition
       • Association between entities that always operate in both directions
     • Participation
       • Entities that participate in relationship
     • The relationship name is in active or passive verb
     • Connectivity
       • Describe the relationship classification
         • Classification includes 1:1, 1:M, and M:N
     • Cardinality
       • In the ERD, cardinality is indicated by placing the appropriate numbers beside the entities, using the format (x,y)
       • definition
         • Express the minimum and maximum number of entity occurences associated with one occurence of related entity
       • The first value (x) represent the minimum number of associated entities
       • The second (y) represent the maximum number of associated entities
     • Relationship Participation
       • Participation in an entity relationship is either optional or mandatory
       • Optional participation
         • Definition
           • One entity occurence does not require a corresponding entity occurence in a particular relationship (verb: may, can)
       • Mandatory participation
         • Definition
           • one entity occurence must have a corresponding occurence in another entity (verb: must)
       • Associative (omposite) Entities
         • Used to represent an M:N relationship between two or more entities
         • It is also called a composite or bridge entity and is a 1:M relationship with the parent entities
         • It is composed of the primary key attributes of each parent entity
         • The composite entity may also contain additional attributes that play no role in connective process
       • Developing an ER diagram
         • Steps to develop ERD
           • Identify the business rules based on the description of operations
           • List all the entities based on given scenario
           • List all the attributes for each entity
           • Assign Primary Key (PK) for each entity
           • Draw line to show relationship between all entities
           • Specify connectivity between entities