System Analysis and Design Lecture 2 PDF

SYSTEM ANALYSIS AND DESIGN (1404704) Lecture 2 Determining System Requirements Course Presentation by Dr. Eman Abd El Reheem PERFORMING REQUIREMENTS DETERMINATION REQUIREMENTS DETERMINATION During requirements...

SYSTEM ANALYSIS AND DESIGN (1404704) Lecture 2 Determining System Requirements Course Presentation by Dr. Eman Abd El Reheem PERFORMING REQUIREMENTS DETERMINATION REQUIREMENTS DETERMINATION During requirements determination, the system analysts gather information on what the system should do from many sources:  From interviews and observations  From computerized sources - Joint Application Design session results, reports from existing systems, displays and reports from system prototype  DELIVERABLES AND OUTCOMES Types of deliverables: Information collected from users Existing documents and files Computer-based information Understanding of Business objective  DETERMINING REQUIREMENTS METHODS Traditional Methods for Determining Requirements Modern Methods for Determining Requirements TRADITIONAL METHODS FOR DETERMINING REQUIREMENTS TRADITIONAL METHODS FOR DETERMINING REQUIREMENTS  Interviewing individuals  Interviewing groups  Nominal Group Technique  Questionnaires  Analyzing Procedures and Other Documents 7 INTERVIEWING INDIVIDUALS One of the primary ways analysts gather information about an information systems project  GUIDELINES FOR EFFECTIVE INTERVIEWING  Plan the interview.  Prepare interviewee: appointment, priming questions, checklist, questions.  Listen carefully and take notes (tape record if permitted).  Type up notes within 48 hours  Do not set expectations about the new system  Seek diverse views. INTERVIEW QUESTIONS Open-ended questions: questions that have no pre-specified answers. Closed-ended questions: questions that ask those responding to choose from among a set of specified responses  CLOSED-ENDED QUESTIONS Closed-ended questions can follow several forms, including these choices:  True or false  Multiple choice (with only one response or selecting all relevant choices)  Rating a response or idea on some scale, say, from bad to good or strongly agree to strongly disagree INTERVIEWING AND LISTENING (CONT.) Typical interview guide  INTERVIEWING GROUPS (CONT.) Interviewing several key people together Advantages More effective use of time Enables people to hear opinions of others and to agree or disagree Disadvantages More difficult to schedule than individual interviews NOMINAL GROUP TECHNIQUE (NGT) A facilitated process that supports idea generation by groups.  Process Members come together as a group, but initially work separately. Each person writes ideas. Facilitator reads ideas out loud, and they are written on a blackboard or flipchart.  NOMINAL GROUP TECHNIQUE (NGT) Group openly discusses the ideas for clarification. Ideas are prioritized , combined, selected, reduced.  NGT as part of JAD effort.  QUESTIONNAIRES Questionnaires are best when many people are involved, each person is to answer roughly the same questions Mostly closed-ended questions  Interviews versus Questionnaires: Interviews provide large amounts of rich, detailed information, but they are expensive to conduct in terms of the time they demand. Questionnaires, on the other hand, can reach many people at once, making them relatively less costly than interviews, but the data collected in this way will not be as rich or as plentiful as is the case with interviews. Both techniques involve careful planning and execution to be successful. ANALYZING PROCEDURES AND OTHER DOCUMENTS By examining existing system and existing documents, system analyst can find out details about current system and system requirements MODERN METHODS FOR DETERMINING REQUIREMENTS MODERN METHODS FOR DETERMINING REQUIREMENTS  Joint Application Design (JAD)  Prototyping 4. 18  PROTOTYPE  Quickly converts requirements to working version of system  Once the user sees requirements converted to system, will ask for modifications or will generate additional requests  Most useful when: User requests are not clear Designs are complex and require concrete form Tools are readily available to build prototype JOINT APPLICATION DESIGN (JAD) Brings users, managers, and analysts work together for several days in a series of intensive meetings to specify or review system requirements. It’s better than traditional techniques because you have all key personnel in one place at one time, saving everyone time and resulting in high levels of system ownership as more people have more of a role in the development process. 4. 18 JOINT APPLICATION DESIGN (JAD) JAD Participants: Session Leader: facilitates group process Users: active, speaking part i cipants Managers: active, speaking participants Systems Analysts: should mostly listen Scribe: record sessi·on activities IS Staff : should mostly listen JOINT APPLICATION DESIGN (JAD)  JOINT APPLICATION DESIGN (JAD)  When a JAD is completed, the final result is a set of documents that detail the workings of the current system.  These requirements definition document generally includes: data model and definition, data input and output requirements. interface requirements, Structuring System Requirements PROCESS MODELING Graphically represent the processes that capture, manipulate, store, and distribute data between a system and its environment and among system components. Utilize information gathered during requirements determination. Processes and data structures are modeled. STRUCTURING SYSTEM REQUIREMENTS Data Flow Diagrams (DFDs) Analysis tool to structure user requirements in a system Graphically represents data movement or flow in an information system and relationships among data flow Evolve from the more general to the more specific DFD SYMBOLS  DFDS Data Flow Drown as a arrow. the route that data takes between the external entities, processes and data stores. Data in motion from one place in a system to another  DFDS Data store Drown as a rectangular. files that hold information for later use, such as a database table. Example: a data store in a data about students, faculty, staff , community users, etc.  DFDS Process performed on data so that they are transformed, changes the data, stored or distributed. Name is a verb phrase  DFDS Source/sink  Drown as a square  Refers to a external entity  Another organization or unit that sends and receives information from the system  A person who interacts with the system, inside or outside  DFD SYMBOLS  Process: work or actions performed on data (inside the system)  Data store: data at rest (inside the system)  Source/sink: external entity interacts with the system (outside the system)  Data flow: arrows depicting movement of data DFD RULES Process  No process can have only outputs.  No process can have only inputs.  A process has a verb phrase label DFD DIAGRAMMING RULES PROCESS No process can have only outputs or only inputs...processes must have both outputs and inputs. Process labels should be verb phrases. DFD RULES Data Store  Data cannot be moved directly from one store to another  Data cannot move directly from an outside source to a data store  Data cannot move directly from a data store to a data sink  Data store has a noun phrase label DFD DIAGRAMMING RULES DATA STORE All flows to or from a data store must move through a process. Data store labels should be noun phrases. DFD RULES Source/Sink  Data cannot move directly from a source to a source.  A source/sink has a noun phrase label DFD DIAGRAMMING RULES SOURCE/SINK Source and sink labels should be noun phrases. DFD RULES Data Flow  A data flow has only one direction of flow between symbols  A fork means that exactly the same data goes from a common location to two or more processes, data stores or sources/sinks DFD DIAGRAMMING RULES DATA FLOW DFD RULES Data Flow  A data flow cannot go directly back to the" same process it leaves. 0  Data flow from a process to a data store means update (insert, delete or change).  Data flow from a data store to a process means retrieve or use.  A data flow has a noun phrase label. L.. FUNCTIONAL DECOMPOSITION An iterative process of breaking a system description down into finer and finer detail. High-level processes described in terms of lower-level sub-processes. DFD charts created for each level of detail  DFD LEVELS Context DFD Overview of the organizational system Level-1 DFD Representation of system's major processes, data flow and data store at high level of detail Level-2 DFD Results from decomposition of Level 1 diagram (show majar flow between entities and the system (too general)) Level-n DFD Results from decomposition of Level n-2 diagram  CONTEXT DIAGRAM OF FOOD ORDERING SYSTEM 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. LEVEL-1 DFD OF FOOD ORDERING SYSTEM Level-1 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.  LEVEL-2 DFD OF FOOD ORDERING SYSTEM Level- 2 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 decomposed in more primitive (lower-level) DFDs if necessary.  LEVEL- N DFD OF FOOD ORDERING SYSTEM Level-n DFD shows the sub- processes of one of the processes in the Level n-1 DFD. This is a Level-3 DFD for Process 4.3. Processes are labeled 4.3.1 4.3.2, etc. If this is the lowest level of the hierarchy, it is called a primitive DFD. DECOMPOSITION OF DFDS Functional decomposition Iterative process of breaking the description of a system/process down into finer and finer detail. Repetitive procedure that creates hierarchically related set of diagrams representing the system. Lowest level is called a primitive DFD Level-N Diagrams A DFD that is the result of n nested decompositions of a series of sub-processes from a process on a level-0 diagram LEVEL-1 DFD SHOWING THE DECOMPOSITION OF PROCESS 1.0 FROM THE LEVEL-0 DIAGRAM FOR FOOD ORDERING SYSTEM DFD BALANCING  The conservation of inputs and outputs to a data flow process when that process is decomposed to a lower level  Balanced means: Number of inputs to lower level DFD equals number of inputs to associated process of higher level DFD Number of outputs to lower level DFD equals number of outputs to associated process of higher-level DFD UNBALANCED DFD Context diagram This is unbalanced because the process of the context diagram has only one Level-1 diagram input but the Level-1 diagram has two inputs. BALANCED DFD Context diagram Level-1 diagram DATA FLOW SPLITTING A composite data flow at a higher level can be split into different processes in the lower level DFD, but no new data can be added. This remains balanced because the same data is involved, but split into two parts. DFD DEVELOPMENT PROCESS Main Steps Determine the processes by making a list of all relevant business activities. Create the context diagram, including all external entities and the major data flow to or from them. Create Level-1 Diagram by analyzing the major activities within the context process. Include the external entities and major data stores. Create a child diagram for each complex process on Level-2 Diagram. Include local data stores and detailed processes. GUIDELINES FOR DRAWING DFDS Completeness DFD must include all components necessary for system,. Consistency The extent to which information contained on one level of a set of nested DFDs is also included on other levels. Iterative Development Analyst should expect to redraw diagram several times before reaching the closest approximation to the system being modeled  GUIDELINES FOR DRAWING DFD Primitive DFDs Lowest level of decomposition Decision has to be made when to stop decomposition Rules for stopping decomposition When each data store represents data about a single entity. When the system user does not care to see any more detail. When every data flow does not need to be split further to show that data are handled in various ways. ASSIGNMENT Retail clothing store in a mall 1. List all relevant sources/sinks, processes, data stores and data flows 2. Draw a context diagram 3. Draw a level-1 diagram 4. Draw a level-2 diagram The deadline on 28/10/2024 PROJECT  Report includes:  What is the problem?  What is the objective, and information requirements from the program?  Draw DFD  Draw ERD  Explain database  program includes:  Source code  User interface