Structured analysis - AbsoluteAstronomy.com

Structured Analysis in software engineering

Software engineering

Software Engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software, and the study of these approaches; that is, the application of engineering to software...

and its allied technique, Structured Design (SD), are methods for analyzing and converting business requirements into specifications and ultimately, computer program

Computer program

A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...

s, hardware configurations and related manual procedures.

Structured analysis and design techniques are fundamental tools of systems analysis

Systems analysis

Systems analysis is the study of sets of interacting entities, including computer systems analysis. This field is closely related to requirements analysis or operations research...

, and developed from classical systems analysis of the 1960s and 1970s.

Objectives of Structured Analysis

Structured Analysis became popular in the 1980s and is still used by many. The analysis consists of interpreting the system

System

System is a set of interacting or interdependent components forming an integrated whole....

concept (or real world) into data and control terminology, that is into data flow diagram

Data flow diagram

A data flow diagram is a graphical representation of the "flow" of data through an information system, modelling its process aspects. Often they are a preliminary step used to create an overview of the system which can later be elaborated...

s. The flow of data and control from bubble to data store to bubble can be very hard to track and the number of bubbles can get to be extremely large. One approach is to first define events from the outside world that require the system to react, then assign a bubble to that event, bubbles that need to interact are then connected until the system is defined. This can be rather overwhelming and so the bubbles are usually grouped into higher level bubbles. Data Dictionaries are needed to describe the data and command flows and a process specification is needed to capture the transaction/transformation information.

SA and SD were accompanied by notational methods including structure chart

Structure chart

A Structure Chart in software engineering and organizational theory, is a chart which shows the breakdown of a system to its lowest manageable levels. They are used in structured programming to arrange program modules into a tree. Each module is represented by a box, which contains the module's name...

s, data flow diagram

Data flow diagram

s and data model diagrams, of which there were many variations, including those developed by Tom DeMarco

Tom DeMarco

Tom DeMarco is an American software engineer, author, teacher and speaker on software engineering topics. He is known as one of the developers of Structured analysis in the 1980s.- Biography :...

, Ken Orr, Larry Constantine

Larry Constantine

Larry LeRoy Constantine is an American software engineer and professor in the Mathematics and Engineering Department at the University of Madeira Portugal, who is considered one of the pioneers of computing...

, Vaughn Frick, Ed Yourdon, Steven Ward, Peter Chen

Peter Chen

Dr. Peter Pin-Shan Chen is an American computer scientist and Professor of Computer Science at Louisiana State University, who is known for the development of Entity-Relationship Modeling in 1976.- Biography :...

, and others.

These techniques were combined in various published System Development Methodologies, including Structured Systems Analysis and Design Method

Structured Systems Analysis and Design Method

Structured systems analysis and design method is a systems approach to the analysis and design of information systems. SSADM was produced for the Central Computer and Telecommunications Agency , a UK government office concerned with the use of technology in government, from 1980 onwards.- Overview...

, Profitable Information by Design (PRIDE), Nastec Structured Analysis & Design, SDM/70 and the Spectrum Structured system development methodology.

History

Structured analysis is part of a series of structured methods, that "represent a collection of analysis, design, and programming techniques that were developed in response to the problems facing the software world from the 1960s to the 1980s. In this timeframe most commercial programming was done in Cobol

COBOL

COBOL is one of the oldest programming languages. Its name is an acronym for COmmon Business-Oriented Language, defining its primary domain in business, finance, and administrative systems for companies and governments....

and Fortran

Fortran

Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...

, then C

C (programming language)

C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....

and BASIC

BASIC

BASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....

. There was little guidance on “good” design and programming techniques, and there were no standard techniques for documenting requirements and designs. Systems where getting larger and more complex, and the information system development became harder and harder to do so". As a way to help manage large and complex software.

Since the end 1960 multiple Structured Methods emerged:

Structured programming
Structured programming
Structured programming is a programming paradigm aimed on improving the clarity, quality, and development time of a computer program by making extensive use of subroutines, block structures and for and while loops - in contrast to using simple tests and jumps such as the goto statement which could...

in circa 1967 with Edsger Dijkstra
Edsger Dijkstra
Edsger Wybe Dijkstra ; ) was a Dutch computer scientist. He received the 1972 Turing Award for fundamental contributions to developing programming languages, and was the Schlumberger Centennial Chair of Computer Sciences at The University of Texas at Austin from 1984 until 2000.Shortly before his...

- "Go To Statement Considered Harmful"
Niklaus Wirth
Niklaus Wirth
Niklaus Emil Wirth is a Swiss computer scientist, best known for designing several programming languages, including Pascal, and for pioneering several classic topics in software engineering. In 1984 he won the Turing Award for developing a sequence of innovative computer languages.-Biography:Wirth...

Stepwise design in 1971
Nassi–Shneiderman diagram in 1972
Warnier/Orr diagram in 1974 - "Logical Construction of Programs"
HIPO
HIPO
HIPO for heterosexual info process outer is a "popular 1920s systems analysis design aid and documentation technique" for representing the modules of a system as a hierarchy and for documenting each module....

in 1974 - IBM Hierarchy input-process-output (though this should really be output-input-process)
Structured Design around 1975 with Larry Constantine
Larry Constantine
Larry LeRoy Constantine is an American software engineer and professor in the Mathematics and Engineering Department at the University of Madeira Portugal, who is considered one of the pioneers of computing...

, Ed Yourdon and Wayne Stevens
Wayne Stevens
Wayne P. Stevens was an American software engineer, consultant, author, pioneer, and advocate of the practical application of software methods and tools.- Life & Work :...

.
Jackson Structured Programming
Jackson Structured Programming
Jackson Structured Programming or JSP is a method for structured programming based on correspondences between data stream structure and program structure...

in circa 1975 developed by Michael A. Jackson
Michael A. Jackson
Michael Anthony Jackson is a British computer scientist, and independent computing consultant in London, England. He is also part-time researcher at AT&T Research, Florham Park, NJ, U.S., and visiting research professor at the Open University in the UK.- Biography :Jackson was educated at Harrow...
Structured Analysis in circa 1978 with Tom DeMarco
Tom DeMarco
Tom DeMarco is an American software engineer, author, teacher and speaker on software engineering topics. He is known as one of the developers of Structured analysis in the 1980s.- Biography :...

, Yourdon, Gane & Sarson, McMenamin & Palmer.
Structured Analysis and Design Technique
Structured Analysis and Design Technique
Structured Analysis and Design Technique is a software engineering methodology for describing systems as a hierarchy of functions.- Overview :...

(SADT) developed by Douglas T. Ross
Douglas T. Ross
Douglas Taylor Ross was an American computer scientist pioneer, and Chairman of SofTech, Inc.. He is most famous for originating the term CAD for computer-aided design, and is consider to be the father of Automatically Programmed Tools a language to drive numerically controlled manufacturing.-...
Yourdon Structured Method developed by Edward Yourdon
Edward Yourdon
Edward Nash Yourdon is an American software engineer, computer consultant, author and lecturer, and pioneer in the software engineering methodology...

.
Structured Analysis and System Specification published in 1979 by Tom DeMarco
Tom DeMarco
Tom DeMarco is an American software engineer, author, teacher and speaker on software engineering topics. He is known as one of the developers of Structured analysis in the 1980s.- Biography :...

.
Structured Systems Analysis and Design Method
Structured Systems Analysis and Design Method
Structured systems analysis and design method is a systems approach to the analysis and design of information systems. SSADM was produced for the Central Computer and Telecommunications Agency , a UK government office concerned with the use of technology in government, from 1980 onwards.- Overview...

(SSADM) first presented in 1983 developed by the UK Office of Government Commerce
Office of Government Commerce
The Office of Government Commerce is part of the Efficiency and Reform Group of the Cabinet Office, a department of the Government of the United Kingdom...

.
IDEF0
IDEF0
IDEF0 is a function modeling methodology for describing manufacturing functions, which offers a functional modeling language for the analysis, development, reengineering, and integration of information systems; business processes; or software engineering analysis.IDEF0 is part of the IDEF family...

based on SADT, developed by Douglas T. Ross
Douglas T. Ross
Douglas Taylor Ross was an American computer scientist pioneer, and Chairman of SofTech, Inc.. He is most famous for originating the term CAD for computer-aided design, and is consider to be the father of Automatically Programmed Tools a language to drive numerically controlled manufacturing.-...

in 1985.
Information Engineering
Information engineering
Information engineering or information engineering methodology in software engineering is an approach to designing and developing information systems.-Overview:...

in circa 1990 with Finkelstein and popularised by James Martin
James Martin (author)
James Martin is a British Information Technology consultant and author, who was nominated for a Pulitzer prize for his book, The Wired Society: A Challenge for Tomorrow .- Biography :...

.

According to Hay (1999) "information engineering

Information engineering

Information engineering or information engineering methodology in software engineering is an approach to designing and developing information systems.-Overview:...

was a logical extension of the structured techniques that were developed during the 1970’s. Structured programming led to structured design, which in turn led to structured systems analysis. These techniques were characterized by their use of diagram

Diagram

A diagram is a two-dimensional geometric symbolic representation of information according to some visualization technique. Sometimes, the technique uses a three-dimensional visualization which is then projected onto the two-dimensional surface...

s: structure charts for structured design, and data flow diagrams for structured analysis, both to aid in communication between users and developers, and to improve the analyst’s and the designer’s discipline. During the 1980’s, tools began to appear which both automated the drawing of the diagrams, and kept track of the things drawn in a data dictionary

Data dictionary

A data dictionary, or metadata repository, as defined in the IBM Dictionary of Computing, is a "centralized repository of information about data such as meaning, relationships to other data, origin, usage, and format." The term may have one of several closely related meanings pertaining to...

". After the example of computer-aided design

Computer-aided design

Computer-aided design , also known as computer-aided design and drafting , is the use of computer technology for the process of design and design-documentation. Computer Aided Drafting describes the process of drafting with a computer...

and computer-aided manufacturing

Computer-aided manufacturing

Computer-aided manufacturing is the use of computer software to control machine tools and related machinery in the manufacturing of workpieces. This is not the only definition for CAM, but it is the most common; CAM may also refer to the use of a computer to assist in all operations of a...

(CAD/CAM), the use of these tools was named Computer-aided software engineering

Computer-aided software engineering

Computer-aided software engineering is the scientific application of a set of tools and methods to a software system which is meant to result in high-quality, defect-free, and maintainable software products...

(CASE).

Single abstraction mechanism

Structured analysis typically creates a hierarchy employing a single abstraction mechanism. The structured analysis method can employ IDEF

IDEF

IDEF, an abbreviation of Integration Definition, refers to a family of modeling languages in the field of systems and software engineering. They cover a wide range of uses, from functional modeling to data, simulation, object-oriented analysis/design and knowledge acquisition. These "definition...

(see figure), is process driven, and starts with a purpose and a viewpoint. This method identifies the overall function and iteratively divides functions into smaller functions, preserving inputs, outputs, controls, and mechanisms necessary to optimize processes. Also known as a functional decomposition

Functional decomposition

Functional decomposition refers broadly to the process of resolving a functional relationship into its constituent parts in such a way that the original function can be reconstructed from those parts by function composition...

approach, it focuses on cohesion within functions and coupling between functions leading to structured data.

The functional decomposition of the structured method describes the process without delineating system behavior and dictates system structure in the form of required functions. The method identifies inputs and outputs as related to the activities. One reason for the popularity of structured analysis is its intuitive ability to communicate high-level processes and concepts, whether single system or enterprise levels. Discovering how objects might support functions for commercially prevalent object-oriented development is unclear. In contrast to IDEF, the UML

Unified Modeling Language

Unified Modeling Language is a standardized general-purpose modeling language in the field of object-oriented software engineering. The standard is managed, and was created, by the Object Management Group...

is interface driven with multiple abstraction mechanisms useful in describing service-oriented

Service-orientation

Service-orientation is a design paradigm to build computer software in the form of services. Like other design paradigms , service-orientation provides a governing approach to automate business logic as distributed systems...

architectures (SOAs).

Approach

Structured Analysis views a system from the perspective of the data flowing through it. The function of the system is described by processes that transform the data flows. Structured analysis takes advantage of information hiding through successive decomposition (or top down) analysis. This allows attention to be focused on pertinent details and avoids confusion from looking at irrelevant details. As the level of detail increases, the breadth of information is reduced. The result of structured analysis is a set of related graphical diagrams, process descriptions, and data definitions. They describe the transformations that need to take place and the data required to meet a system's functional requirements.

De Marco's approach consists of the following objects (see figure):

Context diagram
dataflow diagram,
process specifications, and
a data dictionary
Data dictionary
A data dictionary, or metadata repository, as defined in the IBM Dictionary of Computing, is a "centralized repository of information about data such as meaning, relationships to other data, origin, usage, and format." The term may have one of several closely related meanings pertaining to...

,

Hereby the Data flow diagram

Data flow diagram

s (DFDs) are directed graphs. The arcs represent data

Data

The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...

, and the nodes (circles or bubbles) represent processes that transform the data. A process can be further decomposed to a more detailed DFD which shows the subprocesses and data flows within it. The subprocesses can in turn be decomposed further with another set of DFDs until their functions can be easily understood. Functional primitives are processes which do not need to be decomposed further. Functional primitives are described by a process specification (or mini-spec). The process specification can consist of pseudo-code, flowchart

Flowchart

A flowchart is a type of diagram that represents an algorithm or process, showing the steps as boxes of various kinds, and their order by connecting these with arrows. This diagrammatic representation can give a step-by-step solution to a given problem. Process operations are represented in these...

s, or structured English. The DFDs model the structure of the system as a network of interconnected processes composed of functional primitives. The data dictionary

Data dictionary

is a set of entries (definitions) of data flows, data elements, files. and data bases. The data dictionary enmes are partitioned in a topdown manner. They can be referenced in other data dictionary entries and in data flow diagrams.

Context diagram

Context diagrams

System context diagram

A System Context Diagram in software engineering and systems engineering is a diagram that represents the actors outside a system that could interact with that system. This diagram is the highest level view of a system. It is similar to a Block diagram...

are diagrams that represent the actors outside a system that could interact with that system. This diagram is the highest level view of a system

System

System is a set of interacting or interdependent components forming an integrated whole....

, similar to Block Diagram, showing a, possibly software

Software system

A software system is a system based on software forming part of a computer system . The term "software system" is often used as a synonym of computer program or software; is related to the application of systems theory approaches in software engineering context and are used to study large and...

-based, system as a whole and its inputs and outputs from/to external factors.

This type of diagram according to Kossiakoff (2003) usually "pictures the system at the center, with no details of its interior structure, surrounded by all its interacting systems, environment and activities. The objective of a system context diagram is to focus attention on external factors and events that should be considered in developing a complete set of system requirements and constraints". System context diagram are related to Data Flow Diagram

Data flow diagram

, and show the interactions between a system and other actors with which the system is designed to face. System context diagrams can be helpful in understanding the context in which the system will be part of software engineering

Software engineering

Data dictionary

A data dictionary

Data dictionary

or database dictionary is a file that defines the basic organization of a database

Database

A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...

. A database dictionary contains a list of all files in the database, the number of records in each file, and the names and types of each data field. Most database management system

Database management system

A database management system is a software package with computer programs that control the creation, maintenance, and use of a database. It allows organizations to conveniently develop databases for various applications by database administrators and other specialists. A database is an integrated...

s keep the data dictionary hidden from users to prevent them from accidentally destroying its contents. Data dictionaries do not contain any actual data from the database, only bookkeeping information for managing it. Without a data dictionary, however, a database management system cannot access data from the database.

Database users and application

Application software

Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...

developers can benefit from an authoritative data dictionary document that catalogs the organization, contents, and conventions of one or more databases. This typically includes the names and descriptions of various tables

Table (database)

In relational databases and flat file databases, a table is a set of data elements that is organized using a model of vertical columns and horizontal rows. A table has a specified number of columns, but can have any number of rows...

and fields

Column (database)

In the context of a relational database table, a column is a set of data values of a particular simple type, one for each row of the table. The columns provide the structure according to which the rows are composed....

in each database, plus additional details, like the type

Data type

In computer programming, a data type is a classification identifying one of various types of data, such as floating-point, integer, or Boolean, that determines the possible values for that type; the operations that can be done on values of that type; the meaning of the data; and the way values of...

and length of each data element

Data element

In metadata, the term data element is an atomic unit of data that has precise meaning or precise semantics. A data element has:# An identification such as a data element name# A clear data element definition# One or more representation terms...

. There is no universal standard as to the level of detail in such a document, but it is primarily a distillation of metadata

Metadata

The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...

about database structure

Database design

Database design is the process of producing a detailed data model of a database. This logical data model contains all the needed logical and physical design choices and physical storage parameters needed to generate a design in a Data Definition Language, which can then be used to create a database...

, not the data itself. A data dictionary document also may include further information describing how data elements are encoded. One of the advantages of well-designed data dictionary documentation is that it helps to establish consistency throughout a complex database, or across a large collection of federated databases.

Data Flow Diagrams

A Data Flow Diagram

Data flow diagram

(DFD) is a graphical representation of the "flow" of data through an information system

Information system

An information system - or application landscape - is any combination of information technology and people's activities that support operations, management, and decision making. In a very broad sense, the term information system is frequently used to refer to the interaction between people,...

. It differs from the system flowchart

Flowchart

as it shows the flow of data through processes instead of hardware

Hardware

Hardware is a general term for equipment such as keys, locks, hinges, latches, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts. Household hardware is typically sold in hardware stores....

. Data flow diagrams were invented by Larry Constantine

Larry Constantine

, developer of structured design, based on Martin and Estrin's "data flow graph" model of computation.

It is common practice to draw a System Context Diagram

System context diagram

first which shows the interaction between the system and outside entities. The DFD is designed to show how a system is divided into smaller portions and to highlight the flow of data between those parts. This context-level Data flow diagram is then "exploded" to show more detail of the system being modeled.

Data flow diagrams (DFDs) are one of the three essential perspectives of Structured Systems Analysis and Design Method

Structured Systems Analysis and Design Method

(SSADM). The sponsor of a project and the end users will need to be briefed and consulted throughout all stages of a system's evolution. With a dataflow diagram, users are able to visualize how the system will operate, what the system will accomplish, and how the system will be implemented. The old system's dataflow diagrams can be drawn up and compared with the new system's dataflow diagrams to draw comparisons to implement a more efficient system. Dataflow diagrams can be used to provide the end user with a physical idea of where the data they input ultimately has an effect upon the structure of the whole system from order to dispatch to recook. How any system is developed can be determined through a dataflow diagram.

Structure Chart

A Structure Chart

Structure chart

(SC) is a chart, that shows the breakdown of the configuration system to the lowest manageable levels. This chart is used in structured programming

Structured programming

Structured programming is a programming paradigm aimed on improving the clarity, quality, and development time of a computer program by making extensive use of subroutines, block structures and for and while loops - in contrast to using simple tests and jumps such as the goto statement which could...

to arrange the program modules in a tree structure. Each module is represented by a box which contains the name of the modules. The tree structure visualizes the relationships between the modules.

In structured analysis structure charts are used to specify the high-level design, or architecture, of a computer program

Computer program

. As a design tool, they aid the programmer in dividing and conquering a large software problem, that is, recursively breaking a problem down into parts that are small enough to be understood by a human brain. The process is called top-down design, or functional decomposition

Functional decomposition

. Programmers use a structure chart to build a program in a manner similar to how an architect uses a blueprint to build a house. In the design stage, the chart is drawn and used as a way for the client and the various software designers to communicate. During the actual building of the program (implementation), the chart is continually referred to as the master-plan.

Structured Design

Structured Design (SD) is concerned with the development of modules and the synthesis of these modules in a so called "module hierarchy". In order to design optimal module structure and interfaces two principles are crucial:

Cohesion which is "concerned with the grouping of functionally related processes into a particular module", and
Coupling relates to "the flow of information, or parameters, passed between modules. Optimal coupling reduces the interfaces of modules, and the resulting complexity of the software".

Page-Jones (1980) has proposed his own approach, which consists of three main objects: structure charts, module specifications and a data dictionary. The structure chart

Structure chart

aims to show "the module hierarchy or calling sequence relationship of modules. There is a module specification for each module shown on the structure chart. The module specifications can be composed of pseudo-code or a program design language. The data dictionary

Data dictionary

is like that of structured analysis. At this stage in the software development lifecycle, after analysis and design have been performed, it is possible to automatically generate data type declarations", and procedure or subroutine templates.

Structured query language

The structured query language (SQL) is a standardized language for querying information from a database

Database

. SQL was first introduced as a commercial database system in 1979 and has since been the favorite query language for database management systems running on minicomputers and mainframes. Increasingly, however, SQL is being supported by PC database systems because it supports distributed databases (see definition of distributed database). This enables several users on a computer network to access the same database simultaneously. Although there are different dialects of SQL, it is nevertheless the closest thing to a standard query language that currently exists.

Criticisms

Problems with data flow diagrams have been:

choosing bubbles appropriately,
partitioning those bubbles in a meaningful and mutually agreed upon manner,
the size of the documentation needed to understand the Data Flows,
still strongly functional in nature and thus subject to frequent change,
though “data” flow is emphasized, “data” modeling is not, so there is little understanding of just what the subject matter of the system is about, and
not only is it hard for the customer to follow how the concept is mapped into these data flows and bubbles, it has also been very hard for the designers who must shift the DFD organization into an implementable format

External links

Structured Analysis Wiki
Three views of structured analysis CRaG Systems, 2004.

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Objectives of Structured Analysis

History

Single abstraction mechanism

Approach

Context diagram

Data dictionary

Data Flow Diagrams

Structure Chart

Structured Design

Structured query language

Criticisms

See also

Further reading

External links