System/subsystem Specification - model text

The System/subsystem specification (SSS) specifies the requirements for a system or subsystem and the methods to be used to ensure that each requirement has been met. Requirements pertinent to the system or subsystem external interfaces may be presented in the SSS or in one or more interface requirements specifications (IRSs) and referenced from the SSS. Reference SSSDID for more information.






Prepared for:

Prepared by:

This document contains No. of pages pages

insert here a distribution statement




Insert the "Table of Contents" here.

Consult DI-IPSC-81431 and 'Documentation Standard' when preparing this document.


1.1 Identification.

Identify the system to which this document applies, including, as applicable, identification number(s), title(s), abbreviation(s), version number(s), and release number(s).

1.2 System overview.

State the purpose of the system or subsystem to which this document applies.

1.3 Document overview.

Summarize the purpose and contents of this document.
This document comprises of six sections:

Describe any security or privacy considerations associated with its use.


2.1 Project documents.

Identify the project management systems documents here.
e.g., Project Plan, System Engineering Management Plan, Configuration Management Plan, Documentation Standard, etc.

2.1 Other documents.

2.1 Precedence.

2.1 Source of documents.



This section shall be divided into paragraphs to specify the system requirements, that is, those characteristics of the system that are conditions for its acceptance. Each requirement shall be assigned a project-unique identifier to support testing and traceability and shall be stated in such a way that an objective test can be defined for it.
Each requirement shall be annotated with associated qualification method(s) (see section 4) and, for subsystems, traceability to system requirements (see section 5), if not provided in those sections. The degree of detail to be provided shall be guided by the following rule: include those characteristics of the system that are conditions for system acceptance; defer to design descriptions those characteristics that the acquirer is willing to leave up to the developer. If there are no requirements in a given paragraph, the paragraph shall so state. If a given requirement fits into more than one paragraph, it may be stated once and referenced from the other paragraphs.

3.1 Required states and modes.

If the system is required to operate in more than one state or mode having requirements distinct from other states or modes, this paragraph shall identify and define each state and mode. Examples of states and modes include: idle, ready, active, post-use analysis, training, degraded, emergency, back-up, wartime, peacetime.
The distinction between states and modes is arbitrary. A system may be described in terms of states only, modes only, states within states, or any other scheme that is useful. If no states or modes are required, this paragraph shall so state, without the need to create artificial distinctions. If states and/or modes are required, each requirement or group of requirements in this specification shall be correlated to the states and modes. The correlation may be indicated by a table or other method in this paragraph, in an appendix referenced from this paragraph, or by annotation of the requirements in the paragraphs where they appear.

3.2 System capability requirements.

Itemize the requirements associated with each capability of the system. A "capability" is defined as a group of related requirements. The word capability may be replaced with "function", "subject", "object", "or other term useful for presenting the requirements.

3.2. X (System capability).

Identify the required system capability and itemize the requirements associated with the capability. If the capability can be more clearly specified by dividing it into constituent capabilities, the constituent capabilities shall be specified in subparagraphs.

3.3 System external interface requirements.

Specify the requirements, if any, for the system's external interfaces. This may reference one or more 'Interface Requirements Specifications' (IRSs) or other documents containing these requirements.

3.3.1 Interface identification and diagrams.

3.3. X Interface identification and diagrams.

3.4 System internal interface requirements.

Specify the requirements, if any, imposed on interfaces internal to the system. If all internal interfaces are left to the design or to requirement specifications for system components, this fact shall be so stated. If such requirements are to be imposed, see previous paragraph (3.3) for a list of applicable topics.

3.5 System internal data requirements.

Specify the requirements, if any, imposed on data internal to the system. Include requirements, if any, on databases and data files to be included in the system. If all decisions about internal data are left to the design or to requirements specifications for system components, this fact shall be so stated. If such requirements are to be imposed see 3.3 for a list of topics.

3.6 Adaptation requirements.

3.7 Safety requirements.

3.8 Security and privacy requirements.

3.9 System environment requirements.

3.10 Computer resource requirements.

3.11 System quality factors.

Specify the requirements, if any, pertaining to system quality factors. Examples include quantitative requirements concerning system functionality (the ability to perform all required functions), reliability (the ability to perform with correct, consistent results; such as mean time between failure for equipment), maintainability (the ability to be easily serviced, repaired, or corrected), availability (the ability to be accessed and operated when needed), flexibility (the ability to be easily adapted to changing requirements), portability of software (the ability to be easily modified for a new environment), reusability (the ability to be used in multiple applications), testability (the ability to be easily and thoroughly tested), usability (the ability to be easily learned and used), and other attributes.

3.12 Design and construction constraints.

Specify the requirements, if any, that constrain the design and construction of the system.

3.13 Personnel-related requirements.

3.14 Training-related requirements.

3.15Logistic-related requirements.

3.16Other requirements.

3.17Packaging requirements.

3.18 Precedence and criticality of requirements.



For system-level specifications, this paragraph does not apply. For subsystem-level specifications, this paragraph shall contain:


This section contains information of a general or explanatory nature that may be helpful, but is not mandatory.

6.1 Intended use.

This system/subsystem specification shall ...

6.2 Definitions used in this document.

Insert here an alphabetic list of definitions and their source if different from the declared sources specified in the 'Documentation standard'.

6.3 Abbreviations used in this document.

Insert here an alphabetic list of the abbreviations and acronyms if not identified in the declared sources specified in the 'Documentation Standard'.

6.4 Changes from previous issue.

Will be "not applicable" for the initial issue.

Revisions shall identify the method used to identify changes from the previous issue. i.e., change bars, etc.

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See also system/subsystem specification - DID

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Copyright © by Ken Rigby 1996, 1997, 1998 -- 2003