Logic Modeling Logic and timing are not represented on data flow diagrams or entity-relationship diagrams Processes contain logic - what happens under.

Logic Modeling

• Logic and timing are not represented on data flow diagrams or entity-relationship diagrams

• Processes contain logic - what happens under what conditions

• Logic is modeled per process

• Types of logic: sequence, conditions, iteration

Structured English

• Uses a subset of English

• Uses indentation similar to programming

• Uses process-type verbs like READ, WRITE, GENERATE, CHECK, PRINT

• Verbs and control words in CAPS

• Refers to the data coming in and out of the process

• No specific syntax rules

READ Inventory recordsWHILE NOT End-of-file DO

BEGIN IFIF Quantity-in-stock is less than Minimum-order-quantityTHEN GENERATE new orderELSE DO nothing

END IFEND DO

Structured English Examples

READ next prescriptionSELECT CASE

CASE (prescription for formulated drug)DO send to lab station

CASE (prescription for off-the-shelf drug)DO send to shelving station

CASE (prescription for narcotic drug)DO send to secure station

END CASE

Conditions/ RulesCourses of Action 1 2 3 4Employee type S H H HHours worked - <40 40 >40

Pay base salary XCalculate hourly wage X X XCalculate overtime XProduce absence report X

Decision Tables

1

2

Pay base salary

Calculate hourly wage;Produce absence report

Calculate hourly wage

Calculate hourly wage;Calculate overtime wage

Salaried

Hourly <40

40

>40

Legend1) Type of employee2) Hours worked

Decision Trees

Network Models

• Network Decomposition Diagram– hubs - places where data is stored or processing

is done for users at some other location– workstations - places where a user physically

sits and can access the system remotely

• Hub Connectivity Diagrams– simply says what hubs and external networks

have to exchange data

Network Decomposition Diagram

Set ofWorkstations

System

Hub Hub Hub

Workstation

Workstation

Workstation Workstation Workstation

ExternalNetwork

Hub Connectivity Diagram

Hub

Hub

Hub

50 feet35 miles

ExternalNetwork

3000

mile

s

Simple Example

CustomerOrderingSystem

Server

SystemAdministrator

CreditVerification

Service

OrderTakers

ServerCredit

VerificationService

200 miles

Data Dictionary- Includes:

- descriptions of all pieces of data

- relationships between pieces of data

- Purposes- eliminate ambiguities

- identify links between DFDs and ERD

- clarify how different pieces of data are related

- serves as a standard reference throughout the project

- specify what is contained in data stores and flows

What needs to be defined

Data flows

Data stores

Data elements

Entities

Relationships

Attributes

are collectionsof

are collectionsof

correspond to

Basic parts of a definition

• Name (that appears on the diagram)

• Type (data flow, data store, entity, etc.)

• Description (text)

• Synonyms (other names used for same thing)

• What it contains

• What it is contained in

• Constraints/data type

Data Flow Definition• Name (that appears on the diagram)• Type = data flow• Description (text)• Synonyms• What it contains - list of data elements; lower-level

data flows• What it is contained in - data flow in higher-level

diagram• Constraints - source and destination

Example Data Flow DefinitionName: Customer Record

Type: data flow

Description: The customer information that needs to be stored in the customer DB

Synonyms: none

What it contains: data elements:

customer IDcustomer namecustomer addresscustomer phone

lower-level data flows: none

What it is contained in: none

Constraints:

Source: Process 5, Create Customer Record

Destination: Data Store D3, Customer Master

Data Store Definition• Name (that appears on the diagram, including ID)• Type = data store• Description (text)• Synonyms• What it contains - list of data elements• What it is contained in - n/a• Constraints - physical form, if known

Example Data Store Definition

Name: Customer Master

Type: data store

Description: Information on all customers who have provided this information when placing an order

Synonyms: none

What it contains: data elements:

customer IDcustomer namecustomer addresscustomer phone

What it is contained in: n/a

Constraints: form is a database table

Data Element Definition• Name (does not appear on the diagram)• Type = data element• Description (text)• Synonyms (other data elements and attributes)• What it contains - n/a• What it is contained in (data stores and data flows)• Constraints (format, length, valid values)

Example Data Element Definition

Name: customer name

Type: data element

Description: The last name of a customer who has at one time placed an order

Synonyms: attribute Customer.name

What it contains: n/a

What it is contained in:

data flow Customer Record; data store Customer Master

Constraints: must be a character string with maximum length 15

Entity Definition• Name (that appears on the diagram)• Type = entity• Description (text)• Synonyms• What it contains (attributes)• What it is contained in - n/a• Constraints (identifier)

Example Entity Definition

Name: Customer

Type: entity

Description: Any individual who has at one time placed an order and purchased goods

Synonyms: none

What it contains: attributes Customer_ID, Name, Address, Phone

What it is contained in: n/a

Constraints: Customer_ID must be unique

Relationship Definition• Name (that appears on the diagram)• Type = relationship• Description (text)• Synonyms• What it contains (attributes, including key attributes

of participating entities)• What it is contained in - n/a• Constraints (cardinality, degree, operational

constraints)

Example Relationship

ACCOUNT

account number

balance

ownertype

Has

CUSTOMERNameAddress

Customer_ID Phone8

ChargeCustomerPurchase

D5 Customer Accounts

PurchaseInformation

ERD DFD

CustomerInformation

AccountInformation

Example Relationship Definition

Name: Has

Type: relationship

Description: Associates individual customers with the credit accounts they have with this business, that they can use to purchase goods

Synonyms: data store D5, Customer Accounts

What it contains: attributes Customer.Customer_ID, Account.account_number, owner_type

What it is contained in: n/a

Constraints: binary; many-to-one; mandatory for accounts, but not customers

Attribute Definition• Name (that appears on the diagram)• Type = attribute• Description (text)• Synonyms (other attributes and data elements )• What it contains - n/a• What it is contained in (entities and relationships)• Constraints (format, length, valid values)

Example Attribute Definition

Name: Name

Type: attribute

Description: The last name of a customer who has at one time placed an order

Synonyms: data element customer_name

What it contains: none

What it is contained in: entity Customer

Constraints: must be a character string with maximum length 15