Software Engineering

Lecture 11: System Analysis

Today’s Topics Requirements Analysis & Elicitation Modeling the Problem Domain Prototyping Structured Analysis Models

Analysis: A Bridge Between System Engineering & Software Design

[From SEPA/5e]

Interview Questions “Who is requesting the work?” “Who will use the solution?” “Desired economic benefits?” “Another source for solutions?” “What’s ‘good’ output?” “What problems are addressed?” “Environment of use?” “Special issues or constraints?” Meta-questions re: process

Facilitated Application-Specific Techniques (FAST)

Conduct meetings at neutral site Rules for meetings established Formal agenda, informal discussion “Facilitator” controls meeting “Definition mechanism” agreed upon by

participants

FAST [3]

Goals:• identify problem

• propose elements of a solution

• negotiate different approaches

• specify preliminary set of requirements

• atmosphere: goal-directed

Quality Function Deployment (QFD)

Normal Requirements(explicitly discussed)

Expected Requirements(easy install, good doc)

Exciting Requirements(unexpected, welcome)

Prioritize, document, and discuss with customer

Modeling the Information Domain

Data (numbers, text, etc.) Control (events) Information Content (objects, attributes) Information Flow

(changes to data/control during execution) Information Structure

(internal data and control, relations, etc.)

[From SEPA/5e]

Information Flow and Transformation

Modeling Focus on “what”, not “how” Functional models (HIPO to algorithm

identification) Behavioral models

(program state & changes thereto) Models provide:

• tool for understanding

• focal point for review

• foundation for design

Partitioning

Decompose information, functional, and behavioral domains into subproblems

Vertical: expose more detail Horizontal: decompose into subcomponents

[From SEPA/5e]

Horizontal Partitioning

• functional decomposition

[From SEPA/5e]

VerticalPartitioning

• exposes detail

Essential vs. Implementation View

Essential view• presents the functions to be accomplished, without

implementation details

Implementation view• presents “real-world” manifestation of essential elements

• “current mode of operation”(not a proposed design!)

Prototyping Construct/analyze a prototype:

• to validate requirements

• to show feasibility of solution

Throwaway: discarded before full development Evolutionary: prototype is first version of

finished system

[From SEPA/5e]

The Prototyping Decision Process

StructuredAnalysisModel

[From SEPA/5e]

Structured Analysis

Data Dictionary• descriptions of all data objects

Entity-Relationship Diagram • depicts relations between objects

Data Flow Diagram• how data are transformed

• functions that transform them

Structured Analysis [2] State-Transition Diagram

• states: modes of behavior

• transitions: trigger state change

Data Object Description• note attributes of each object

Process Specification• describe each process in DFD

Control Specification• describe each state/transition in STD

[Fro

m S

EPA

/5e]

Data Objects, Attributes, Relationships

Tabular Representation of Data Objects

[From SEPA/5e]

[Fro

m S

EPA

/5e]

Relationships

[Fro

m S

EPA

/5e]

Cardinality and Modality

[Fro

m S

EPA

/5e]

Simple ERD, Data Object Table

[Fro

m S

EPA

/5e]

ExpandedERD

[Fro

m S

EPA

/5e]

Data ObjectType Hierarchy

[Fro

m S

EPA

/5e]

AssociativeData Objects

Information Flow Model

[From SEPA/5e]• data flow diagram

[Fro

m S

EPA

/5e]

BehavioralModel

• control flow diagram

[Fro

m S

EPA

/5e]

State-TransitionDiagram

Specifications Control Specification

• state-transition diagram

• program activation table: “a combinatorial specification of behavior”

Process Specification• narrative text

• pseudocode or program design language (PDL)

[Fro

m S

EPA

/5e]

Program Activation Table

• which processes are invoked when an event occurs?

Specifications [2] Data Dictionary (for each object):

• Name & Aliases

• Where Used / How Used

• Content Description

• Supplementary Information• data types, default values, restrictions, limitations, etc.

Questions?