Specification (technical standard)
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A specification is an explicit set of requirements to be satisfied by a material, product, or service. [1]
Contents |
[edit] Use
In engineering, manufacturing, and business, it is vital for suppliers, purchasers, and users of materials, products, or services to understand and agree upon all requirements. A specification is a type of a standard which is often referenced by a contract or procurement document. It provides the necessary details about the specific requirements.
Specifications may be written by government agencies, standards organizations (ASTM, ISO, CEN, etc), trade associations, corporations, and others.
A product specification does not necessarily prove the product to be correct. Just because an item is stamped with a specification number does not, by itself, indicate that the item is fit for any particular use. The people who use the item (engineers, trade unions, etc) or specify the item (building codes, government, industry, etc) have the responsibility to consider the available specifications, specify the correct one, enforce compliance, and use the item correctly. Validation of suitability is necessary.
An example of a US Federal specification is FIPS-PUB 159, Detail Specification for 62.5-μm Core diameter/125-μm Cladding Diameter Class Ia Multimode Optical Fibers. (Source: from Federal Standard 1037C and from MIL-STD-188)
[edit] Content
A specification might include:
- Descriptive title and scope of the specification
- Date of last effective revision and revision designation
- Person, office, or agency responsible for questions on the specification, updates, and deviations.
- The significance or importance of the specification and its intended use.
- Terminology and definitions to clarify the meanings of the specification
- Test methods for measuring all specified characteristics
- Material requirements: physical, mechanical, electrical, chemical, etc. Targets and tolerances.
- Performance testing requirements. Targets and tolerances.
- Drawings, photographs, or technical illustrations
- Workmanship
- Certifications required.
- Safety considerations and requirements
- Environmental considerations and requirements
- Quality requirements, Sampling (statistics), inspections, acceptance criteria
- Person, office, or agency responsible for enforcement of the specification.
- Completion and delivery.
- Provisions for rejection, reinspection, rehearing, corrective measures
[edit] Process capability considerations
A good engineering specification, by itself, does not necessarily imply that all products sold to that specification actually meet the listed targets and tolerances. Actual production of any material, product, or service involves inherent variation of output. With a normal distribution, the tails of production may extend well beyond plus and minus three standard deviations from the process average.
The process capability of materials and products needs to be compatible with the specified engineering tolerances. Process controls must be in place and an effective Quality management system, such as Total Quality Management, needs to keep actual production within the desired tolerances.
Effective enforcement of a specification is necessary for it to be useful.
[edit] Construction specifications in North America
Specifications in North America form part of the contract documents that accompany and govern the construction of a building. The guiding master document is the National MasterFormat. It is a consensus document that is jointly sponsored by two professional organisations: Construction Specifications Canada and Construction Specifications Institute.
While there is a tendency to believe that "Specs overrule Drawings" in the event of discrepancies between the text document and the drawings. The actual intent is for drawings and specifications to be complimentary with neither taking precedence over the other.
The Specifications fall into 50 "Divisions", or broad categories of work involved in construction. The "Divisions" are subdivided into "Sections", that address specific workscopes. For instance, firestopping is addressed in Section 078400 - Firestopping. It forms part of the Division 7, which is Thermal and Moisture Protection. Division 7 also addresses building envelope and fireproofing work. Each Section is subdivided into three distinct areas: "General", "Products" and "Execution". The National MasterFormat system has been uniformly applied to residential, commercial and much though not all industrial work.
Specifications can be another "performance-based", whereby the specifier restricts the text to stating the performance that must be achieved in each Section of work, or "prescriptive", whereby the specifier indicates specific products, vendors and even contractors that are acceptable for each workscope.
While North American specifications are usually restricted to broad descriptions of the work, European ones can include actual work quantities, including such things as area of drywall to be built in square metres, like a bill of materials. This type of specification is a collaborative effort between a specwriter and a quantity surveyor. This approach is unusual in North America, where each bidder performs his or her own quantity survey on the basis of both drawings and specifications.
Specification writing is a professional trade with its own professional designations, such as "CCS", which means "Certified Construction Specifier". Specwriters can be either employees of or sub-contractors to architects. Specwriters frequently meet with manufacturers of building materials who seek to have their products "specified" on upcoming construction projects so that contractors can include their products in the estimates leading to their proposals.
[edit] Food and drug specifications
Pharmaceutical products can usually be tested and qualified by various Pharmacopoeia. Current existing pronounced standards include:
- British Pharmacopoeia
- European Pharmacopoeia
- Japanese Pharmacopoeia
- The International Pharmacopoeia
- United States Pharmacopoeia
If any pharmaceutical product is not covered by the above standards, it can be evaluated by the additional source of Pharmacopoeia from other nations, from industrial specifications. or from standardized formulary such as
A similar approach is adopted by the food manufacturing, of which Codex Alimentarius ranks the hightest standards, followed by regional and national standards. [2]
The coverage of food and drug standards by ISO is currently less fruitfull and not yet put forward as an urgent agenda due to the tight restrictions of regional or national constitution [3], [4]
Specifications and other standards exist not only for the food or pharmaceutical product but also for the processing machinery, quality processes, packaging, logistics (cold chain), etc.
[edit] Software development
[edit] Formal specification
A formal specification is a mathematical description of software or hardware that may be used to develop an implementation. It describes what the system should do, not (necessarily) how the system should do it. Given such a specification, it is possible to use formal verification techniques to demonstrate that a candidate system design is correct with respect to the specification. This has the advantage that incorrect candidate system designs can be revised before a major investment has been made in actually implementing the design. An alternative approach is to use provably correct refinement steps to transform a specification into a design, and ultimately into an actual implementation, that is correct by construction.
[edit] Program specification
A program specification is the definition of what a computer program is expected to do. It can be informal, in which case it can be considered as a blueprint or user manual from a developer point of view, or formal, in which case it has a definite meaning defined in mathematical or programmatic terms. In practice, most successful specifications are written to understand and fine-tune applications that were already well-developed, although safety-critical software systems are often carefully specified prior to application development. Specifications are most important for external interfaces that must remain stable.
[edit] Functional specification
In software development, a functional specification (also, functional spec or specs or functional specifications document (FSD)) is the set of documentation that describes the behavior of a computer program or larger software system. The documentation typically describes various inputs that can be provided to the software system and how the system responds to those inputs.
[edit] References
[edit] Further reading
- Pyzdek, T, "Quality Engineering Handbook", 2003, ISBN 0824746147
- Godfrey, A. B., "Juran's Quality Handbook", 1999, ISBN 007034003
- "Specifications for the Chemical And Process Industries", 1996, ASQ Quality Press, ISBN:0-87389-351-4
- ASTM E29-06b Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
[edit] See also
- Construction Specifications Institute
- Defense Standard
- Diagnostic design specification
- Formal specification
- List of ISO standards
- MasterFormat
- Manufacturing test requirement design specification
- Open standard
- Performance testing
- Process specification
- Product design specification, detailed specification (created before a product is designed) of what it is required to do.
- Publicly Available Specification
- Requirements analysis
- Submittals (construction)
- Shop drawing
- Statistical interference
- Tolerance (engineering)
- Verification
- Verification and Validation
