Modeling System RequirementsSystems Analysis and Design

Models and Modeling

• A model is a representation of some aspect of the system being built.

• The purpose of models:– models help the analyst clarify and simplify the

design– Models assist in the communication between

system users and developers and foster understanding

Models and Modeling

• Types of models– Mathematical Models• Formulas that describe technical aspects of the system

– Descriptive Models• Narrative memos, reports or lists that describe some

aspect of a system

– Graphical Models• Diagrams and schematic representations of some

aspect of the system

Models Used in Systems Analysis and Design

• Models created during analysis phase– Entity-Relationship Diagram– Activity Diagram

• Models created during the design phase– Screen/Report Layout– System Flowchart– Database Design/Schema– Network Diagram– Structure Chart (HIPO)

Entity Relationship Diagram

• An entity relationship diagram is a model used to define the data storage requirement. – Data entities • The things the system needs to store information about• Contains an identifier and attributes

Entity Relationship Diagram

• A simple ERD:

Customer Order

A customer can place zero or more orders

Order must be placed by exactly one customer

Entity Relationship Diagram

• Cardinality Symbols of Relationships

Exactly One (Mandatory)

Zero or One (Optional)

Zero or more (Optional)

One or more (Mandatory)

Entity Relationship Diagram

• An expanded ERD with attributes shown:

CustomerCust NumberNameAddressPhone

OrderOrder IDOrder Date Amount

Order ItemItem ID

QuantityPrice

Screen/Report Layout

Database Design/Schema

Network Diagram

• A computer network diagram is a schematic depicting the nodes and connections amongst nodes in a computer network

Structure Chart (HIPO)

• A structure chart is a design tool that pictorially shows the relation between processing modules in computer software.