SYSTEMS ANALYSIS DESIGN PHASE 2 SYSTEMS ANALYSIS Analyzing

SYSTEMS ANALYSIS & DESIGN PHASE 2 SYSTEMS ANALYSIS Analyzing Requirements

Chapter 4 Analyzing Requirements SYSTEMS ANALYSIS & DESIGN 3 E PHASE 2 2

Objectives PHASE 2 3 à Explain the structured analysis process and identify its elements à Describe the symbols used in data flow diagrams and explain the rules for their use à Explain the sequence of data flow diagrams, from general to specific, and what each data flow contains SYSTEMS ANALYSIS & DESIGN 3 E

Objectives PHASE 2 4 à Explain how to level and balance a set of data flow diagrams à Draw a complete set of data flow diagrams for an information system à Describe how a data dictionary is used and what it contains SYSTEMS ANALYSIS & DESIGN 3 E

Objectives PHASE 2 5 à Demonstrate the use of structured English, decision tables, and decision trees to develop information system process descriptions à Explain the relationships among data flow diagrams, the data dictionary, and process descriptions SYSTEMS ANALYSIS & DESIGN 3 E

Introduction à Systems analysis phase has three stages à Requirements determination (Chapter 3) à Requirements analysis (Chapter 4) à Evaluation of alternatives (Chapter 5) SYSTEMS ANALYSIS & DESIGN 3 E PHASE 2 6

Structured Analysis PHASE 2 7 à Examines inputs, outputs, and processes à Common method à Process-centered technique à Uses three main tools à Data flow diagrams (DFDs) à Data dictionary à Process descriptions à Tools can be applied using computer-aided software engineering (CASE) tools SYSTEMS ANALYSIS & DESIGN 3 E

PHASE 2 8 Data Flow Diagrams à Data flow diagrams (DFDs) are graphical aids that describe an information system à DFDs represent a logical model that shows what a system does, not how it does it SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -1

PHASE 2 9 Data Flow Diagrams à Data flow diagram symbols à Four basic symbols à Process à Data flow à Data store à External entity à Two popular symbol sets à Gane and Sarson à Yourdon SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -2

Data Flow Diagrams PHASE 2 10 à Process symbol à Symbol is a rectangle with rounded corners à Documented with process descriptions à Receive input data and produces output à Output has a different form, or content, or both à Details are shown in a process description à In DFDs the process symbol appears as a black box, underlying details not shown SYSTEMS ANALYSIS & DESIGN 3 E

PHASE 2 11 Data Flow Diagrams à Data flow symbol à Symbol is a line with an arrowhead showing direction à A path for data to move from one part of the system to another à Might represent one or many pieces of data à At least one data flow must enter and exit each process SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -3

PHASE 2 12 Data Flow Diagrams à Data flow symbol à Incorrect process and data flow combinations cause problems à Spontaneous generation (miracle) à Black hole à Gray hole SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -4

PHASE 2 13 Data Flow Diagrams à Data store symbol à Symbol is a rectangle open on the right side à Data store also is called a data repository à Represents data that is retained for later processing à Must be connected to a process with a data flow à Must have at least one outgoing and incoming data flow Click to see Figure 4 -5 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -6

PHASE 2 14 Data Flow Diagrams à External entity symbol à Symbol is a square, usually shaded à Represents a person, organization, or other system that provides data or receives output from the system à External entities are called terminators à Source (supplies data to the system) à Sink (receives data from the system) Click to see Figure 4 -7 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -8

PHASE 2 15 Data Flow Diagrams à External entity symbol à Symbol is a square, usually shaded à Represents a person, organization, or other system that provides data or receives output from the system à External entities are called terminators à Source (supplies data to the system) à Sink (receives data from the system à Must follow specific rules for connecting DFD symbols SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -9

PHASE 2 16 Data Flow Diagrams à Context diagrams à Top-level view that shows the overall boundaries of the system à Represent the results of fact-finding à One process symbol, numbered 0 (zero) is drawn in the center à Data flows connect the process to the entities à Abbreviated symbols can be used to identify entities Click to see Figure 4 -10 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -11

PHASE 2 17 Data Flow Diagrams à Conventions for data flow diagrams à Each context diagram must fit on one page à Process name in the context diagram should be the name of the information system à Use unique names within each set of symbols à Do not cross lines à Use abbreviated identifications à Use a unique reference number for each process symbol SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -12

Data Flow Diagrams PHASE 2 18 à Diagram 0 à Displays more detail than the context diagram à Shows entities, major processes, data flows, and data stores SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -13

Data Flow Diagrams PHASE 2 19 à Shows entities, major processes, data flows, and data stores à Other characteristics à Can contain diverging data flows à Exploded (partitioned or decomposed) version of process 0 à Diagram 0 is the child of the parent context diagram à Also can be called an overview or level 0 diagram à Can contain functional primitives Click to see Figure 4 -14 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -15

PHASE 2 20 Data Flow Diagrams à Lower-level diagrams à Usually necessary to show more detail SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -16

PHASE 2 21 Data Flow Diagrams à Lower-level diagrams à Usually necessary to show more detail à Design must consider à Leveling à Balancing à Data stores SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -17

Data Flow Diagrams PHASE 2 22 à Leveling à Process of drawing increasingly detailed diagrams à Also called exploding, partitioning, or decomposing SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -18

Data Flow Diagrams PHASE 2 23 à Balancing à Maintains consistency among an entire set of DFDs à Parent’s input and output data flows are preserved on the child SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -19

Data Flow Diagrams PHASE 2 24 à Data stores à Might not appear on higher-level DFDs à Are shown on the highest-level DFD that has two or more processes using that data store SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -20

PHASE 2 25 TRADEOFF à Which technique is better: top-down or bottom-up? à Most analysts start at the top à Draw the context diagram à Diagram 0 and lower-level diagrams next à Others start at the bottom à Identify functional primitives, data stores, external entities, and data flows à Work up until diagram 0 is reached à Results must be clear and easily understood Click to see Figure 4 -21 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -23

A KEY QUESTION PHASE 2 26 à Based on the rules in the text, how many problems do you see in Figure 4 -22? SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -22

PHASE 2 27 Data Dictionary à Also called data repository à Documents specific facts about the system à Data flows à Data stores à External entities à Processes à Data elements (data items, fields) à Records (data structures) SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -24

Data Dictionary PHASE 2 28 à Using CASE tools to document the system à Can help create and maintain a data dictionary à Various tools are available à Visible Analyst is a popular example à Key objective is to provide clear, comprehensive information about the system SYSTEMS ANALYSIS & DESIGN 3 E

PHASE 2 29 Data Dictionary à Documenting the data elements à Must document every data element SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -25

PHASE 2 30 Data Dictionary à Documenting the data elements à Must document every data element à Standard form or CASE tool can be used à All major characteristics must be recorded and described Click to see Figure 4 -26 a SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -26 b

PHASE 2 31 Data Dictionary à Documenting the data flows à Must document every data flow à Standard form or CASE tool can be used à All major characteristics must be recorded and described SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -27

PHASE 2 32 Data Dictionary à Documenting the data stores à Must document every data store à Standard form or CASE tool can be used à All major characteristics must be recorded and described SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -28

PHASE 2 33 Data Dictionary à Documenting the processes à Must document every process à Standard form or CASE tool can be used à All major characteristics must be recorded and described SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -29

PHASE 2 34 Data Dictionary à Documenting the external entities à Must document every external entity à Standard form or CASE tool can be used à All major characteristics must be recorded and described SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -30

Data Dictionary PHASE 2 35 à Documenting the records à Must document every record à Standard form or CASE tool can be used à All major characteristics must be recorded and described SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -31

Data Dictionary PHASE 2 36 à Data dictionary reports à Data dictionary is a central storehouse for documentation à Using this data, you can produce many valuable reports SYSTEMS ANALYSIS & DESIGN 3 E

Process Description Tools PHASE 2 37 à Process description documents a functional primitive, using modular design à Modular design uses three logical structures à Sequence à Selection à Iteration SYSTEMS ANALYSIS & DESIGN 3 E

Process Description Tools PHASE 2 38 à Structured English à Subset of standard English SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -32

Process Description Tools PHASE 2 39 à Structured English à Subset of standard English à Describes process logic à Use only standard sequence, selection, and iteration structures à Use indentation for readability à Use a limited vocabulary SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -33

PHASE 2 40 Process Description Tools à Decision tables à Show a logical structure that describes process logic à Every logical combination is shown initially à Results then can be combined and simplified à Programmers can use decision tables in developing code Click to see Figure 4 -34 Click to see Figure 4 -35 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -36

PHASE 2 41 Process Description Tools à Decision trees à Graphical representation that shows a decision table’s conditions, actions, and rules à Logic structure is shown horizontally à Easy to construct and understand à Decision table is better in complex situations Click to see Figure 4 -37 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -38

TRADEOFF PHASE 2 42 à Logical vs. physical models à Relationship between physical and logical models: first study facts, then logical analysis à Four-model approach offers many advantages à Physical model of current system à Logical model of new system à Physical model of new system à Four-model approach can be time-consuming and expensive SYSTEMS ANALYSIS & DESIGN 3 E

A KEY QUESTION PHASE 2 43 à Is it proper to consider physical implementation questions during the systems analysis phase? à Is Rick going off on a tangent? à What are the issues? SYSTEMS ANALYSIS & DESIGN 3 E

SOFTWEAR, LIMITED PHASE 2 44 à The SWL team completed the fact-finding process à Rick and Carla are ready to prepare a logical model of the system SYSTEMS ANALYSIS & DESIGN 3 E

PHASE 2 45 SOFTWEAR, LIMITED à Data flow diagrams à Rick and Carla prepared a draft context diagram Click to see Figure 4 -39 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -40

SOFTWEAR, LIMITED PHASE 2 46 à Data flow diagrams à Rick and Carla prepared a draft context diagram à Various revisions resulted in final version SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -41

SOFTWEAR, LIMITED PHASE 2 47 à Data flow diagrams à Rick and Carla prepared a draft context diagram à Various revisions resulted in final version à Next steps à Analysts prepared diagram 0 SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -42

SOFTWEAR, LIMITED PHASE 2 48 à Data flow diagrams à Rick and Carla prepared a draft context diagram à Various revisions resulted in final version à Next steps à Analysts prepared diagram 0 à Rick partitioned the ESIP subsystem à Carla developed other lower-level diagrams à Logical model was completed à Physical design issues were considered SYSTEMS ANALYSIS & DESIGN 3 E Click to see Figure 4 -43

PHASE 2 49 SOFTWEAR, LIMITED à Data dictionary and process descriptions à Rick and Carla’s activities à Documented the ESIP subsystem à Met with Amy Calico to review the final model Click to see Figure 4 -44 Click to see Figure 4 -46 Click to see Figure 4 -45 Click to see Figure 4 -47 Click to see Figure 4 -48 SYSTEMS ANALYSIS & DESIGN 3 E

SOFTWEAR, LIMITED PHASE 2 50 à Next steps à Meet with SWL users to review the model à Obtain input, make adjustments, get approval à Complete the payroll system model à Continue work on system requirements document SYSTEMS ANALYSIS & DESIGN 3 E