Structured Analysis Methods and Tools M. M. Pickard, PhD. Department of Computer Science

Overview Methods Tools

Structured Analysis Methods Data Models Information Flow Models Functional Models Behavior Models

Structured Analysis Tools Data Models Entity Relationship Diagrams Data Dictionary Information Models and Functional Models Data Flow Diagrams Control Flow Diagrams Ward and Mellor Extensions Hatley and Pirbhai Extensions

Structured Analysis Tools Behavioral Models Process Descriptions

Entity Relationship Diagrams Used to show the relationship between data entities Cardinality relative numbers of data entities Modality whether data entity is required in the relationship

Data Dictionary Purpose?

Data Dictionary Purpose? Often supported by CASE tool To define and describe all data elements To serve as a central repository of information about the system’s data To organize information about contents of data flows, data stores, and, possibly, external entities and processes. Often supported by CASE tool

Data Dictionary Data element documentation name aliases type length output format acceptable values formula Source security user comments

Data Dictionary (possible components) Data flow information Data store information Process information External entity information Data structure information

Data Flow Diagram (DFD) Shows how data moves through an information system. Logical model What the system does, not how it does it Does NOT show program logic Does NOT explicitly show processing sequence

DFD Methods Gane and Sarson Yourdon

DFD Symbols - Yourdon Process Data Flow Data Store External Entity

DFD - Symbols (Gane & Sarson) Process Data Flow Data Store External Entity

DFD Process Symbol Receives input data and produces output that has a different content or form. Process name: verb followed by a singular noun, optional adjective. Create invoice

DFD Data Flow Symbol A path for data to move from one part of the system to another. Data flow name: noun and optional adjective. invoice

DFD Process Symbol rules A process symbol must have at least one input symbol AND one output symbol. A process symbol can have more than one input symbol and more than one output symbol. A process can connect any other symbol.

DFD Data Flow Symbol rules A data flow must have a process symbol on at least one end. Avoid:

Process/Data Flow Mistakes Spontaneous generation (miracle) Black hole Create invoice invoice Hours worked Calc. Gross pay Pay rate

Process/Data Flow Mistakes Gray hole (insufficient input information to create output) Calc. Gross pay Date of birth Gross pay Pay rate

DFD - Data Store Used to represent a situation when data must be retained in order for a process to use it later. Data store name: plural name consisting of noun and optional adjectives Freshmen

DFD - External Entity A person, department, outside organization, or other information system that provides data or receives output from the system. External entity name: a singular noun bank

Control Flow Diagram Similar to DFD Shows control flow, not information flow May link to CSPEC State Transition Diagram (STD) Process Activation Table (PAT)

Process Description Tools and Methods Structured English Decision Tables Decision Trees

Process Description Tools and Methods Structured English Based on three building blocks of structured programming and design

Process Description Tools and Methods Structured English Based on three building blocks of structured programming and design: sequence, selection, iteration Uses indentation for readability and to indicate logical hierarchy Standard, limited vocabulary

Process Description Tools and Methods Decision (Logic) Tables Used to show complex logic Tables have four quadrants Condition stubs Condition entries Action stubs Action entries A “rule” is a single column

Process Description Tools and Methods Decision (Logic) Tables Simplification Rules having the same outcome, but differing by one condition may be combined. Use a dash to replace the differing condition. Rules that have mutually exclusive conditions (cannot occur) may be carefully eliminated. Linkage The final action of a rule may send us to another table.

Process Description Tools and Methods Decision Trees Effective way to present a combination of simple decisions

Summary Entity Relationship Diagrams Data Flow Diagrams Control Flow Diagrams Data Dictionary Process Descriptions