data flow diagrams

data flow diagrams shows how data moves through an

information system but does not show program logic or processing steps

provides a logical model that shows what the system does, not how it does it

data flow diagrams notation

use four basic symbols that represent processes, data flows, data stores, and external entities

Gane and Sarson symbol set Yourdon symbol set

referenced by using all capital letters for the symbol name

DFD notation

DATA STORE

PROCESS

DATA FLOW

EXTERNALENTITY

DATA FLOW

DATA FLOW

DATA FLOW

DATA STORE

EXTERNALENTITY

PROCESSGane &Sarson

Yourdon

DFD notation process symbol

receives input data and produces output that has a different content, form, or both

contain the business logic, also called business rules

referred to as a black box data flow symbol

represents one or more data items

DFD notation data store symbol

represent data that the system stores logical representation (physical

characteristics of data store are unimportant)

external entity symbol represents the source or sink of data

modeling with DFDs: basic steps step 1: draw a context diagram

context diagram – represents the system as a single process (process 0)

step 2: draw a diagram 0 DFD diagram 0 - exploded view of process 0;

zooms in on the context diagram and shows major processes, data flows, and data stores; must retain all the connections that flow into and out of process 0

modeling with a DFD: basic steps step 3: draw the lower-level diagrams

functional decomposition of diagram 0 observe leveling – use a series of

increasingly detailed DFDs to describe the information system

observe balancing – maintain the input and output data flows of the parent DFD on the child DFD

modeling with DFDs guidelines for drawing DFDs

context diagram should fit on one page use the name of the information system as

the process name in the context diagram use unique names within each set of

symbols do not cross lines provide a unique name and reference

number for each process obtain as much user input and feedback as

possible

modeling with DFDs other syntactic rules

avoid the following combinations of data flow and process

spontaneous generation black hole gray hole

an external entity should be connected by a data flow to a process only

data stores cannot be connected to each other

modeling with DFDs other concepts

naming conventions conservation of data diverging data flows converging data flows composite data flow control flow (e.g., time)

Example: Context Diagram

GRADING SYSTEM

STUDENTRECORDSSYSTEM

STUDENT

INSTRUCTOR

FINAL GRADE

CLASS LIST

GRADE REPORT

SUBMITTED WORK

GRADED WORK

GRADE PARAMETERS

0

Example: Diagram 0

STUDENTRECORDSSYSTEM

STUDENT

INSTRUCTOR

GRADINGDETAIL

CLASS LIST

GRADE REPORT

SUBMITTED WORK

GRADED

WORK

GRADE PARAMETERS

GRADEBOOKD1

ASSIGNFINAL

GRADE

2

GRADESTUDENT

WORK

3

ESTABLISHGRADEBOOK

1

PRODUCEGRADEREPORT

4

CLASSGRADEBOOK

CLASS DETAIL

FINAL GRADE

STUDENTGRADE

DFD levels

Context diagram

Level 0 diagram

Level 1 diagram

Level 2 diagram

4-model approach (classical)

Current Proposed

Logical

physical aspects of system are removed as much as possible;current system is reduced to data and processes that transform them

includes additional functions;obsolete functions are removed; inefficient data flows are reorganized

Physical

processes labels include the technology (people or systems) used to process the data;data flows and data stores are labeled with the actual name of the physical media on which data flow or in which data are stored

represents the physical implementation of the new system

data dictionary data elements must be documented in a

data dictionary so that clear, comprehensive information about the data and processes that make up the system are stored

data dictionary data flow attributes

name or label description alternate name(s) origin destination data structure volume and frequency

data dictionary data store characteristics

data store name or label description alternate name(s) data structure volume and frequency

data dictionary process characteristics

process name or label description process number process description

data dictionary external entity characteristics

entity name description alternate name(s) input data flows output data flows

data dictionary to document attributes, a data structure

is used data structure – specific arrangement of

data attributes that define a data store or a single instance of a data flow

notation = + { } [ ] ()

data dictionary: example

ORDER = ORDER NUMBER + ORDER DATE +

[CUSTOMER NUMBER|CORPORATE ACCOUNT] + SHIP ADDRESS + BILL ADDRESS + {PRODUCT} +

AMOUNT

PRODUCT = PRODUCT NUMBER + DESCRIPTION +

QUANITY ORDERED + PRICE + EXTENDED PRICE

SHIP ADDRESS = ADDRESS

BILL ADDRESS = ADDRESS

ADDRESS = (POBOX NUMBER) + STREET + CITY +

[STATE|PROVINCE] + (COUNTRY) + ZIPCODE

ORDERS = {ORDER}

decomposition diagram depicts the partitioning of the system

into logical subsystems or processes shows the top-down functional

decomposition of a system used as a planning tool for the DFD also known as a hierarchy chart

decomposition diagram

GRADINGSYSTEM

ESTABLISHGRADEBOOK

ASSIGN FINAL

GRADE

GRADESTUDENT

WORK

TASK 1 TASK 2

PRODUCEGRADEREPORT

process description describes the logic of primitive processes may be represented in the following

forms: structured English decision table decision tree

process description structured English

use the three logical building blocks sequence selection iteration

use indentation for readability use standard terms used in the data

dictionary and specific words that describe the processing rules

process description structured English

examples Profits = Revenues - Expenses Generate Inventory Report Add Product record to Products IF Customer Not in Customers

THEN Add Customer to CustomersELSE Add Current Sale to Customer’s Total Sales Add Total Sales to Customer balance in Customers

FOR EACH Customer in CustomersDelete Customer with matching

Customer ID

process description decision tables

alternative way to describe business rules or processing that involve a complex set of conditions

shows a logical structure, with all possible combinations of conditions and resulting actions

rows represent conditions and possible outcomes; columns indicate which combinations of conditions result in specific actions

combination of conditions may result in more than one outcome

process description decision tables

example

Conditions and Actions

Rule 1 Rule 2

Rule 3 Rule 4

type of check personal

payroll

personal

payroll

check amount > 1000

yes - no -

company accredited by X

- yes - no

cash the check X X

do not cash the check X X

process description decision trees

Graphical representation of the conditions, actions, and rules found in a decision table

choice between a decision table or decision tree is a matter of personal preference

process description decision trees

example

other process analysis tools

event-driven approach

use case analysis tool used to describe a business

task and how the user (actor) interacts with the system to accomplish the task

may be represented in narrative or graphical form

no standard template for documenting detailed use cases

analysts are encouraged to use templates that work for them or the project they are on

use case example

Name: Place New OrderUse-Case ID: UC123Source: Requirement 1.00Description: A club member submits a new

order for products. The member’s account standing is validated. When the availability of products is verified, a packing order is sent to the warehouse for it to prepare the shipment. Back orders are created for products not in stock. On completion, the member is sent an order confirmation.

use case example

Precondition: The party making the order must be a member

Trigger: A new order is submittedBasic flow: Member provides order and

payment information. All information are verified ….

Result: An order confirmation is generated and sent to the club member

use case sections Use Case Name Iteration Description Preconditions Triggers Basic course of events Alternative paths Postconditions Business rules Notes Author and date Additional sections such as assumptions,

exceptions, recommendations, technical requirements

event-response list depicts the business events that the

system must respond to employ use case analysis contains information on:

actor that initiates the event event trigger or input response or output

event decomposition diagram map the events to the decomposition serves as an outline for the lower-level

data flow diagrams

system diagram merged events depicted in the data flow

diagram a single diagram may represent the

entire system may be a collection of DFDs representing

a set of events for a major component of the system(e.g., a process in diagram 0)

modern structured analysis draw the context DFD of the proposed

system make the corresponding functional

decomposition diagram and diagram 0 create an event-response or use-case list draw an event DFD for each event * merge event DFDs into a system diagram draw detailed, primitive DFDs for the more

complex events update the data dictionary make the process descriptions