SYSTEMS ANALYSIS AND DESIGN ITDB 2101 HAND OUT # 3 1

2 MAINTENANCE CONVERSION CONSTRUCTION TESTING PROBLEM RECOGNITION FEASIBILITY STUDY ANALYSIS DESIGN THE SYSTEMS DEVELOPMENT LIFE CYCLE (SDLC), also known as the WATERFALL MODEL

STEP 1: PROBLEM RECOGNITION STEP Name Problem Recognition Major Function To establish that a problem exists in the system. Output PROBLEMS TO BE SOLVED; WHY DO WE NEED A BETTER SYSTEM.– Permission to conduct feasibility Study WHO ARE INVOLVED? Systems Analyst, Users (Staff) and Managers of the Company Usually known as the PLANNING STEP.

STEP 2: FEASIBILITY STUDY STEP NameFeasibility Study Major Function ??? OUTPUT Feasibility Report and Risk Analysis WHO ARE INVOLVED? Systems Analyst

STEP 3: ANALYSIS STEP Name ANALYSIS Major Function To study the present system very carefully, study the requirements of the new computerized system, and to create models of the old and the new system. The objective is to clearly understand the present system, learn what is needed, and discover the shortcomings or faults that must be corrected or modified

DATA FLOW DIAGRAM (DFD) DATA FLOW DIAGRAMS (DFD) – graphical representation to show the flow of data within the system. - shows the processes in the system

DATA FLOW DIAGRAM (DFD) Purpose/Objective The purpose of data flow diagrams is to provide a bridge between users and systems developers. Graphical: Eliminating need of thousands of words. Logical Representations: Modeling WHAT a system does, rather than physical model showing HOW it does it.

2 CATEGORIES OF DFD 1.LOGICAL DATA FLOW DIAGRAM 2.PHYSICAL DATA FLOW DIAGRAM

2 CATEGORIES OF DFD 1.LOGICAL DATA FLOW DIAGRAM- Focuses on the business and how the business operates. It describes the events that happens and the data required and produced in each event. 2. PHYSICAL DATA FLOW DIAGRAM- Shows how the system will be implemented.

SYMBOLS OF DFD 1.ENTITY- represents either the SOURCE or the DESTINATION of data. Example: A person, another system or an organization who send or receive data to and from the system SYMBOL:

SYMBOLS OF DFD 2.DATA FLOW- represents movement or the flow of data. SYMBOL:

SYMBOLS OF DFD 3.PROCESS- represents an activity or a process that transforms or manipulates the data. Note: A process transforms incoming data flow into outgoing data flow). SYMBOL:

SYMBOLS OF DFD 4.DATA STORE- represents data that is saved on some file or in a table. Represents the STORAGE of data. SYMBOL:

RULES IN CONSTRUCTING DFDs ENTITY RULE # 1: Data cannot move directly from an entity to another entity. It must be moved by a PROCESS. RULE # 2: An entity should have a NOUN phrase level.

RULES IN CONSTRUCTING DFDs PROCESS RULE # 1: A process should have at least one input and at least one output. RULE # 2: A process should have a VERB phrase level.

RULES IN CONSTRUCTING DFDs DATA FLOW RULE # 1: A data flow should only have one direction of flow between symbols. RULE # 2: A fork in a data means that exactly the same data goes from a common location to two or more different processes, data stores, or sources (this usually indicates different copies of the same data going to different locations)..

RULES IN CONSTRUCTING DFDs DATA FLOW RULE # 3: A data flow cannot go directly back to the same process it leaves.. RULE # 4: A data flow to a data store means update (delete or change). RULE # 5: A data flow from a data store means retrieve or use. RULE # 6: A data flow has a noun phrase label. More than one data flow noun phrase can appear on a single arrow as long as all of the flows on the same arrow move together as one package.

RULES IN CONSTRUCTING DFDs DATA STORE RULE # 1: Data cannot move directly from one data store to another data store. Data must be moved by a process. RULE # 2: Data cannot move directly from an entity to a data store. Data must be moved by a process. RULE # 3: Data cannot move directly from a data store to an entity. Data must be moved by a process. RULE # 4: A data store has a noun phrase level.

STEPS IN CONSTRUCTING DFDs 1.Start with the Context Diagram 2. Identify the functions to be performed 3. Show the information flow between functions and identify data stores and external entities 4. Repeatedly elaborate on the DFD ( bottom up and top down )

CONTEXT DIAGRAMS A context diagram provides the most general view of an information system. Emphasis is on the relationship between the system and its environment. Consist of a single process symbol representing the whole system, entities and data flow.

STEPS IN CONSTRUCTING CONTEXT DIAGRAMS 1. Start by placing a single process symbol at the center of the page. The symbol represents the entire information system, and you identify it as process Then place the external entities around the process and use data flows to connect the entities to the central process. 3. Do not show any data stores in a context diagram because data stores are internal to the system.

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