Information Systems Analysis and Design

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Information Systems

Analysis and Design

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Systems Modeling

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Enterprise Model graphically represents

organizational entities and the relationships between

entities

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A process model represents a system’s functions

(data flow diagrams)

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A data model represents a system’s data and the

relationships between data elements (entity

relationship diagram)

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An object model represents a system’s classes

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Process Modeling

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Graphically represent the processes that capture,

manipulate, store, and distribute data between a

system and its environment and among system

components

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Utilize information gathered during requirements

determination

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Pizza Delivery Example

Custome

r

Chef

Sales

Delivery

Databa

se

1. Coupon, order address payment type 2. wait time 3. order details 5. order 6. order done 8. Pizza 10. Pizza 11. Payment 9. Pizza collected 12. Payment received 7. address 4. confirmation

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Doors-R-Us Service Example

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Process:

Salespeople Customer Receptionist Quote Dispatcher Installer Accounts Receivable Clerk 1. 2. 3. 4. 5. 6. 7. Materials Manager 8. 9. 10. 11. Bill Work Order

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Doors-R-Us Process Explanation

1. Salespeople get potential customers familiar with company/services

2. When potential customer needs a door service, they call HQ, get the receptionist

3. Receptionist finds estimator (HQ /road) to visit customer and assess situation

4. Estimator inspects site and submits quote to warehouse manager 5. If customer decides to use Doors-R-Us, calls HQ (receptionist) to

request service

6. Receptionist finds dispatcher to schedule the work 7. Dispatcher and customer agree on time for service

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Doors-R-Us Process Explanation

8. Dispatcher gets needed supplies from Materials Manager

9. Dispatcher sends an installer to get the replacement door and install it

10. Installer writes up a work order and submits to A/R Clerk 11. A/R Clerk sends bill to Customer

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Process Modeling

Deliverables and Outcomes

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Context data flow diagram (DFD)

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Scope of system

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DFDs of current physical and logical system

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Enables analysts to understand current system

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DFDs of new logical system

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Technology independent

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Show data flows, structure, and functional

requirements of new system

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Data Flow Diagram (DFD)

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A picture of the movement of data between

external entities and the processes and data

stores within a system

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Difference from system flowcharts:

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DFDs depict logical data flow independent of

technology

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Data Flow Symbols (cont.)

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Data Store

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Depicts data at rest

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May represent data in

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File folder

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Computer-based file

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Notebook

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The name of the store as well as the number

are recorded in between lines

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Data Flow Symbols (cont.)

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Process

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Depicts work or action performed on data so

that they are transformed, stored or distributed

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Number of process as well as name are

recorded

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Data flow: arrows depicting movement of data

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Data Flow Symbols (cont.)

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Source/Sink

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Depicts the origin and/or destination of the

data

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Sometimes referred to as an external entity

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Drawn as a square symbol

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Name states what the external agent is

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Because they are external, many

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DFD Diagramming Rules

Process

No process can have only outputs or only inputs…processes must have both outputs and inputs.

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DFD Diagramming Rules

Data Store

Data store labels should be noun phrases. All flows to or from a data store must move through a process.

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DFD Diagramming Rules

Source/Sink

Source and sink labels should be noun phrases. No data moves directly between external entities without going through a process.

Interactions between external entities without

intervening processes are outside the system and therefore not represented in the DFD.

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DFD Diagramming Rules

Data Flow

Bidirectional flow between process and data store is represented by two separate arrows. Forked data flow must refer to exact same data item (not different data items) from a common

location to multiple destinations.

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DFD Diagramming Rules

Data Flow (cont.)

Joined data flow must refer to exact same data item (not different data items) from multiple

sources to a

common location. Data flow cannot go directly from a process to itself, must go through intervening

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DFD Diagramming Rules

Data Flow (cont.)

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Data flow from a process to a data store

means update (insert, delete or change).

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Data flow from a data store to a process

means retrieve or use.

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Functional Decomposition

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An iterative process of breaking a system

description down into finer and finer detail

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High-level processes described in terms of

lower-level sub-processes

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DFD Levels

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Context DFD

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Overview of the organizational system

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Level-0 DFD

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Representation of system’s major processes at high

level of abstraction

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Level-1 DFD

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Results from decomposition of Level 0 diagram

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Level-n DFD

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Context Diagram

Context diagram shows the system boundaries, external entities that interact with the system, and major

information flows between entities and the system.

NOTE: only one process symbol, and no data stores shown.

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Level-0 DFD

Level-0 DFD shows the

system’s major processes, data flows, and data stores at a high level of

abstraction.

Processes are labeled 1.0, 2.0, etc. These will be decomposed into more primitive (lower-level) DFDs.

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Level-1 DFD

Level-1 DFD shows the sub-processes of one of the processes in the Level-0 DFD. This is a Level-1 DFD for Process 4.0.

Processes are labeled 4.1, 4.2, etc. These can be further

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Level-n DFD

Level-n DFD shows the sub-processes of one of the processes in the Level n-1 DFD. This is a Level-2 DFD for Process 4.3.

Processes are labeled 4.3.1, 4.3.2, etc. If this is the

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Nested DFD

2.0 EE1 1.0 D1 EE1 1.1 2.1 2.2 2.3 D 1 D 2 1.2

Level 0

Level 1

1.2.1 _1.2.2

Level 2

Level 1

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A Simple DFD Example:

Customer Order Process for CD On-Line

Customers select the CDs they would like to order and

communicate their selected CD item numbers and their customer

account number to CD On-Line. Based on the customer’s

selection, the order is processed by calculating the order total amount.

The order total and customer account number as well as the

customer’s old credit balance (from the customer credit database) are used to update the customer’s new credit balance. The new

balance should be recorded on the customer credit database.

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A Simple DFD Example:

Customer Order Process for CD On-Line (cont’d)

The detailed order data from order processing and updated customer credit balance information are used to prepare a customer invoice and invoice information is updated. Detailed

invoice data are used to prepare a shipping list and the invoice is

sent to the customer on-line. The shipping list information is sent to UPS. (Based on a partnership relationship between CD

On-Line and UPS, UPS warehouses the CDs and ships the CDs to the customers based on the shipping list).

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Translating into DFD Vocabulary

■ External Entities

■ Customer

■ UPS

■ Internal Entity: CD On-Line

■ Data Store

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Translating into DFD Vocabulary

■ Process

■ Compute order total

■ Update customer credit account balance ■ Prepare invoice

■ Prepare shipping list

■ Data Flows

■ CD item numbers

■ Customer account number ■ Old/New balance

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DFD Balancing

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The conservation of inputs and outputs to a data flow

process when that process is decomposed to a lower

level

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Balanced means:

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Number of inputs to lower level DFD equals number of

inputs to associated process of higher-level DFD

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Number of outputs to lower level DFD equals number

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Unbalanced DFD

This is unbalanced because the process of the context diagram has only one input but the Level-0 diagram has two inputs. 1 input

1 output

2 inputs 1 output

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Balanced DFD

These are balanced because the numbers of inputs and outputs of context diagram process equal the number of inputs and outputs of

1 input 2 outputs

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Balanced DFD (cont.)

These are balanced because the numbers of inputs and outputs to Process 1.0 of the Level-0 diagram equals the number of inputs and outputs to the Level-1 diagram.

1 input 4 outputs

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Data Flow Splitting

A composite data flow at a higher level may be split if different parts go to different processes in the lower level DFD.

This remains balanced because the same data is involved, but split into two parts.