Interface Control Document
From Wikipedia, the free encyclopedia
In systems engineering [1] and software engineering, an Interface Control Document (ICD) is a document that describes the interface(s) to a system or subsystem. An ICD may describe the inputs and outputs of a single system, e.g. "The Wikipedia Interface Control Document." An ICD may also describe the interface between two systems or subsystems, e.g. "The Doghouse to Outhouse Interface Control Document." An ICD may describe the complete interface protocol from the lowest physical elements (e.g., the mating plugs, the electrical signal voltage levels) to the highest logical levels (e.g., the level 7 application layer of the ISO model), or some subset thereof. The purpose of the ICD is to communicate all possible inputs to and all potential outputs from a system for some potential or actual user of the system.
Interface control documents are a key element of systems engineering as they define and control the interface(s) of a system, and thereby bound its requirements.
An application programming interface is a form of ICD, in that it describes how to access the functions and services provided by a system via an interface. If a system producer wants others to be able to use the system, an ICD (or equivalent) is a worthwhile investment.
An ICD should only describe the interface itself, and not the characteristics of the systems which use it to connect. The function and logic of those systems should be described in their own design documents if required. In this way, independent teams can develop the connecting systems which use the interface specified, without regard to how other systems will react to data and signals which are sent over the interface. For example, the ICD must include information about the size and format of the data, but not the meaning of the data, in the sense that the ICD describes how the recipient should react to received data.
An adequately defined ICD will allow one team to test its implementation of the interface by simulating the opposing side with a simple communications simulator. Not knowing the business logic of the system on the far side of an interface makes it more likely that one will develop a system that does not break when the other system changes its business rules and logic. Thus, good modularity and abstraction leading to easy maintenance and extensibility are achieved.
Critics of ICDs and systems engineering in general often complain of the emphasis on documentation[2] [3]. ICDs are often present on "document-driven projects," but may be useful on agile projects as well (although not explicitly named as such)[1][2] . An ICD need not be a textual document. It may be an (evolving) table of goes-intos and comes-out-ofs, a dynamic database representing each subsystem as a DB view, a set of interaction diagrams, etc.
ICDs are often used where subsystems are developed asynchronously in time, since they provide a structured way to communicate information about subsystems interfaces between different subsystem design teams.[3][4][5][6].
[edit] References
- ^ Wolter J. Fabrycky, Benjamin S. Blanford, "Systems Engineering and Analysis," Prentice-Hall, 2005
- ^ Fowler, M.; J. Highsmith (July 2001). The Agile Manifesto. Dr. Dobb's Journal. Retrieved on May 11, 2006., "Yes, physical documentation has heft and substance, but the real measure of success is abstract: Will the people involved gain the understanding they need?"
- ^ Ambler, S.W. (March 2005). Agile Modeling and eXtreme Programming (XP). AgileModeling.com. Retrieved on May 11, 2006., "...verbal communication between team members reduces the need for documentation within the team."
