2.8 The Complex Method SSADM


		Annex 2
		2.8 The Complex Method SSADM

SSADM - Structured Systems Analysis and Design Method

Contents
1 Brief Description
2 Tabular Comparison
3 Specification of the Allocation
4 Literature

Contents		1 Brief Description 2 Tabular Comparison 3 Specification of the Allocation 4 Literature

1 Brief Description

During the beginning of the Eighties, the complex method SSADM (Structured Systems Analysis and Design Method) was developed on behalf of the British government by the consulting company LBMS-Learmonth & Burchett Management Systems in cooperation with CCTA (Central Computer Telecommunications Agency). In 1983, SSADM was declared as the standard to be applied for DP development projects of the British government. Since then, it has been permanently upgraded. The present valid SSADM version is Version 4 (since July 1990) /Downs, 1992/.

The application of SSADM aims at the development of information systems on the basis of database systems and less at the development of real-time-oriented software. Therefore, the method concentrates on data flows, data models, and-as a specialty-the chronological life cycles of entities.

Contrary to the strict separation of procedure and method in the software development standard of the German Federal Armed Forces, a lifecycle process model has been integrated into the method in SSADM.

The lifecycle process model of SSADM supplies both detailed procedures and instructions for analysis and design in connection with software generation (SD1 - System Requirements Analysis to SD5 SW - Detailed SW Design) in the following areas:

which activities must be realized when (three-leveled structure in phases, steps, and tasks),
how the activities are to be realized (Method/Techniques/Tools) and
where and in which form the results are to be recorded (documentation).

However, all implementation and integration activities have been excluded on purpose. In the same way are the accompanying activities of submodels PM, CM, and QA not subject of SSADM but distributed to special methods (e. g. PRINCE, CRAMM).

The following comparison refers to the methodical components of SSADM in the sense of the GD 251. In SSADM, they are referred to as Techniques. These techniques include:

Requirement definition
Contains a general instruction with regard to the definition of requirements.

Dialog design
The "Dialog Design" consists of two steps. In a first step ("dialog identification") the dialogs of the application to be modeled are identified from the point of view of the later user. The "dialog design" is realized at some later date at which menu structures and dialog sequences are developed from the input/output of the application functions.

Data flow modeling
The data flow modeling is used to describe how the DFD processes of the application are communicating with each other and with the environment. The data flow diagrams in SSADM are predominantly used for the documentation and less for the support of an information system design.

Logical data modeling
The technique "Logical data modeling" is based on E/R models. The E/R model represents the entities relevant for an application, together with the corresponding relationships. For the functions identified during the analysis the access path to the E/R model is recorded.

Business system options
Business system options are text descriptions of the information system to be realized. Therefore, they can be considered as a product as well. The required selection for the later implementation must be made from the business system options.

Function definition
In SSADM, functions are the interface between analysis and design. During the analysis phase, identified and logically interacting DFD processes are grouped into functions by taking into consideration the application requirements.

Relational data analysis
Within the scope of the relational data analysis, the entities of the data model are transformed into relations, key attributes are defined, and the normalization is realized.

Specification prototyping
In SSADM, prototyping is predominantly used for assessing the requirements with regard to accuracy and consistency and less for an evolutionary application development. The future user is to have the opportunity to make individual comments about the user interface or the planned functionality as early as possible.

Entity event modeling
Entity Event Modeling is the interface between the data side (E/R model) and the functions based on DFD processes. It checks which externally initiated events refer to the application to be realized, how it must react with regard to the functions, and which entities are affected by the processing of the event.

Technical system options
The character of technical system options corresponds to those of the business system options. The topics are technical aspects of the application to be realized, though.

Logical database process design
A logical database process design specifies the internal structure of the processes accessing the database. In this connection, the data analysis (access paths in the E/R model) and the entity event modeling (Entity Life Histories) are used as a basis.

Physical data design
The logical data model available in a normalized relational form is converted into a physical design.

Physical process specification
Within the scope of the physical process specification, software modules are specified that are used to realize the identified functions. The module structure has to be as detailed as a programming specification.

2 Tabular Comparison

The following table compares the basic methods of the GD 251 with the methodical components of SSADM. In the case where there is no entry in the right column of the table, SSADM has no corresponding component. Otherwise, an entry refers to the corresponding part in the literature. Section 3 of the comparison contains an explanation for the entry. Entries identified by (*) refer to basic methods completely covered by SSADM. These are not further described in section 3.

Comparison of the Basic Methods and the Methodological Components of SSADM
AUD - Audit
ACC - Analysis of Covert Channels
BAR - Bar Plan
TREE - Tree Diagram
BBTD - Black Box Test Case Design
CRC - Class Responsibility Collaboration
DIAL - Dialog Design Modeling	Dialog Design /Downs, 1992/ chap. 3.4
DFM - Data Flow Modeling	Data Flow Modeling /Downs, 1992/ chap. 3.5
DNAV - Data Navigation Modeling	Logical Data Modeling /Downs, 1992/ chap. 3.6
DVER - Design Verification
ELH - Entity Life History	Entity Event Modeling /Downs, 1992/ chap. 3.11
ER - E/R Modeling	Logical Data Modeling /Downs, 1992/ chap. 3.6 (*)
DTAB - Decision Table Technique
EVT - Earned Value Method
EXPM - Expertise Model
FCTD - Functional Decomposition	Data Flow Modeling /Downs, 1992/ chap. 3.5
FMEA - Failure Mode Effect Analysis
FNET - Function Net Modeling
FS - Formal Specification
IAM - Interaction Modeling
CFM - Control Flow Modeling
COM - Class/Object Modeling
LOGM - Logical DB Modeling	Relational Data Analysis /Downs, 1992/ chap. 3.9
MODIAG - Module Diagrams
NORM - Normalization	Relational Data Analysis /Downs, 1992/ chap. 3.9 (*)
NPT - Network Planning Technique
BA - Benefit Analysis
ODT - Object Design Technique
OGC - Organizational Chart
PCODE - Pseudocode	Logical Database Process Design /Downs, 1992/ chap. 3.13
PRODIAG - Process Diagrams
PVER - Program Verification
PIM - Process Interaction Modeling
REV - Review
SIMU - Simulation Models
EMOD - Estimation Models
SSM - Subsystem Modeling
STAT - Static Analysis
STRD - Structured Design	Entity Event Modeling Logical Database Process Design /Downs, 1992/ chapters 3.11 and 3.13
SBM - System Behavior Models
T - Test
TRDA - Trend Analysis
UCM - Use Case Modeling
WBTD - White Box Test Case Design
STM - State Transition Modeling
STMO - State Modeling in the OO Field
RELM - Reliability Models

Table 2.8: Basic Methods-SSADM
3 Specification of the Allocation

Method Corresponding
Component
in SSADM Explanation
DIAL
Dialog Design Modeling /Downs, 1992/ chap. 3.4 "Dialog design", p. 96 The method Dialog Design has two "subtechniques":

within the scope of the "dialog identification", the first step identifies the users and the functionality they request for the information system to be realized,

in the second step there is a logic "dialog design" in which information flows from and to the information system are described.

The generation of the mask layouts or the implementation of the dialogs are not a subject of the method.
DFM
Data Flow Modeling /Downs, 1992/ chap. 3.5 "Data flow modeling", p. 103 The data flow modeling in SSADM covers the basic method DFM completely. In addition to the graphical means of representation "process", "terminator", "data flow", and "data store" required in DFM, so-called physical flows exist in SSADM to describe the material flow between users (terminators) and the system to be modeled (processes). They are used for the user-level description and are only applied on the highest level in data flow diagrams.
DNAV
Data Navigation Modeling /Downs, 1992/ chap. 3.6 "Logical data modeling", "Enquiry access paths", p. 136 Based on the E/R diagram and the identified functions of the information system, the name of the query is defined for all database queries to be realized, the initiating event and the data affected by the query (key, selection criteria), and the path through the data model at the time of the query execution are described.
ELH
Entity Life History /Downs, 1992/ chap. 3.11 "Entity event modeling", "Entity Life History", p. 170 All of the possible operational sequences are graphically described for each entity type during the life cycle of that entity. Means of representation are Structure Charts. ELHs are used to check the completeness of the functional description, to describe interdependencies between functions, and to derive test cases.
FCTD
Functional Decomposition /Downs, 1992/ chap. 3.5 "Data flow modeling", p. 103 The functional decomposition is implicitly contained in technique "Data Flow Modeling". The processes identified during the analysis of the data flows are hierarchically refined on lower levels. The processes generated during the data flow modeling can be arranged into a tree structure.
LOGM
Logical DB Modeling /Downs, 1992/ chap. 3.9 "Relational data analysis", p. 149 Technique "relational data analysis" completely covers the basic method LOGM for the area of relational database systems. The result of the E/R model conversion are tables describing the keys and attributes of the entities. Relationships between entities are (after prior normalization) realized by means of external keys.
PCODE
Pseudocode /Downs, 1992/ chap. 3.13 "Logical database process design", p. 198 The logical database process design is used to describe processes that are accessing a database. Processes receiving or sending data via the user interface or those mapping technical aspects are not described.
The result of this description is a Process Structure Diagram which is upgraded by operations and control structures.
STRD
Structured Design /Downs, 1992/ chap. 3.11 "Entity event modeling" p. 170; chap. 3.13 "Logical database process design", p. 198 The Structure Charts from STRD are applied at various places in SSADM. On the one hand, Entity Life Histories are illustrated with the help of Structure Charts, on the other hand they are utilized in connection with the description of the structure of processes.

4 Literature
/Downs, 1992/ Structured Systems Analysis and Design Method, Application and Context

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Method	Corresponding Component in SSADM	Explanation
DIAL Dialog Design Modeling	/Downs, 1992/ chap. 3.4 "Dialog design", p. 96	The method Dialog Design has two "subtechniques": within the scope of the "dialog identification", the first step identifies the users and the functionality they request for the information system to be realized, in the second step there is a logic "dialog design" in which information flows from and to the information system are described. The generation of the mask layouts or the implementation of the dialogs are not a subject of the method.
DFM Data Flow Modeling	/Downs, 1992/ chap. 3.5 "Data flow modeling", p. 103	The data flow modeling in SSADM covers the basic method DFM completely. In addition to the graphical means of representation "process", "terminator", "data flow", and "data store" required in DFM, so-called physical flows exist in SSADM to describe the material flow between users (terminators) and the system to be modeled (processes). They are used for the user-level description and are only applied on the highest level in data flow diagrams.
DNAV Data Navigation Modeling	/Downs, 1992/ chap. 3.6 "Logical data modeling", "Enquiry access paths", p. 136	Based on the E/R diagram and the identified functions of the information system, the name of the query is defined for all database queries to be realized, the initiating event and the data affected by the query (key, selection criteria), and the path through the data model at the time of the query execution are described.
ELH Entity Life History	/Downs, 1992/ chap. 3.11 "Entity event modeling", "Entity Life History", p. 170	All of the possible operational sequences are graphically described for each entity type during the life cycle of that entity. Means of representation are Structure Charts. ELHs are used to check the completeness of the functional description, to describe interdependencies between functions, and to derive test cases.
FCTD Functional Decomposition	/Downs, 1992/ chap. 3.5 "Data flow modeling", p. 103	The functional decomposition is implicitly contained in technique "Data Flow Modeling". The processes identified during the analysis of the data flows are hierarchically refined on lower levels. The processes generated during the data flow modeling can be arranged into a tree structure.
LOGM Logical DB Modeling	/Downs, 1992/ chap. 3.9 "Relational data analysis", p. 149	Technique "relational data analysis" completely covers the basic method LOGM for the area of relational database systems. The result of the E/R model conversion are tables describing the keys and attributes of the entities. Relationships between entities are (after prior normalization) realized by means of external keys.
PCODE Pseudocode	/Downs, 1992/ chap. 3.13 "Logical database process design", p. 198	The logical database process design is used to describe processes that are accessing a database. Processes receiving or sending data via the user interface or those mapping technical aspects are not described. The result of this description is a Process Structure Diagram which is upgraded by operations and control structures.
STRD Structured Design	/Downs, 1992/ chap. 3.11 "Entity event modeling" p. 170; chap. 3.13 "Logical database process design", p. 198	The Structure Charts from STRD are applied at various places in SSADM. On the one hand, Entity Life Histories are illustrated with the help of Structure Charts, on the other hand they are utilized in connection with the description of the structure of processes.