Models for Open System Protocol Development : A Technical Report (1994)

11. Taxonomy and ISP Issues

11.1 General

By 1987, a special Group on Functional Standardization, the SGFS, was established under ISO JTC1 to sort through the issues of functional standards (also sometimes called functional profiles). The SGFS was chartered to develop the concepts involved with functional standardization, methodology, and procedures for achieving functional standardization, and with the execution of some of those procedures.

The SGFS developed a new type of document, the International Standardized Profile, ISP, which has the status of an ISO International standard. The SGFS also produced ISO Technical Report TR 10000, Framework and Taxonomy of International Standardized Profiles, which describes in detail the purpose and structure of an ISP and the taxonomy of ISPs.

11.2 Profiles and ISPS

A set of one or more base standards, and, where applicable, the identification of chosen classes, subsets, options and parameters of those base standards, necessary for accomplishing a particular function.

Following the definition is the note: "An ISP includes the specification of one or more profiles".

The ISO TR 10000 defines an ISP as:

An Internationally agreed to, harmonized document which identifies a standard or group of standards, together with options and parameters, necessary to accomplish a function or set of functions.

There is an important difference between the concept of profile and ISP. An ISP is a document, and it has the status of an international standard. A profile is simply a group of standards, without any concrete representation. In fact ISO TR 10000 seems to view a profile as an abstract object and an ISP as its physical manifestation (or more generally, as the physical manifestation of one or more profiles). The following text from ISO TR 10000-1 supports this interpretation:

The concept of a profile ... is considered first in an abstract sense ... then extended to include defining its relationship to other profiles .. . Finally, since a profile has to have a concrete existence in order for it to be used effectively, these conceptual aspects are related to a formal documentation system." (Here, "formal documentation system" means an ISP).

There are three other differences in the definitions of profile and ISP worth noting (but not of great significance). First, an ISP refers to "options and parameters" while a profile refers to "classes, subsets, options and parameters". This discrepancy is probably unintentional. Secondly, an ISP refers to parameters, etc. "necessary to accomplish a function or set of functions" while the profile definition instead says "necessary for accomplishing a particular function". The reason for this difference is that an ISP may represent several profiles. Third, the ISP definition refers to "standards", and the profile definition refers to "base standards". The ISP might specify other ISPs as well as base standards, while a profile may only specify base standards.

11.2.1 Purposes of Profiles

Identifying the base standards, together with appropriate classes, subsets, options and parameters necessary to accomplish identified functions for purposes such as interoperability.

In the phrase "for purposes such as interoperability", the use of "such as" implies that profiles exist for more than just interoperability. This point is important because in the narrow view, profiles exist simply to restrict the choices in the standards. According to that view, for a given application protocol there should be a single profile, everyone should use it, and this is the way to achieve global interoperability. ISO TR 10000 takes a broader view: yes, it is true that profiles narrow the options and in so doing, promote interoperability, but also, different environments, communities, or functions may require different profiles.

Another "purpose" cited is:

... providing a system of referencing the various uses of base standards which is meaningful to both users and suppliers ...

Here the key term is "both users and suppliers". Profiles are obviously applicable to users, because users develop profiles, in contrast to the base OSI standards, which are developed primarily by suppliers (SR and ILL are notable exceptions). But profiles are intended also for suppliers so that they will have specifications to build to.

Two other purposes of profiles cited in ISO TR 10000 relate to procurement and conformance testing. Just as profiles are intended to provide a supplier with a specification for implementation, they are also intended to be used for reference in a procurement. profiles are also intended to promote uniformity in the development of conformance tests.

11.2.2 Elements of a Profile

• A set of base standards to be used together
  
• How they are to be used together
  
• Usage details for each of the base standards

"A set of base standards" would be for example, the SR, ACSE, Presentation, and Session protocols. "How they are used together" refers to aspects such as mappings between the protocols. For example, an SR profile might specify: "the Initialize APDU will be carried within the ACSE A-associate". "Particular details of each of the base standards" refers to requirements lists, or IPRLs (International Profile Requirement List).

"A set of base standards" can be interpreted in two ways: the above example (SR, ACSE, Presentation, Session) selects one "specific" application protocol (SR) along with a set of protocols which constitute the supporting upper layer stack. However, "A set of base standards" might include a collection of "specific" application protocols to be used together, for example, SR and ILL. The latter may also be specified by application contexts.

"How they are used together" referring to mappings, etc. is also considered the province of application contexts. Thus there is still apparently some overlap between the concepts of profile and application context.

A profile definition also includes the following elements:

• A statement of scope, function, and purpose
  
• Scenarios of interoperation
  
• A statement of conformance requirements
  

"Conformance to a profile" is analogous to "conformance to a protocol". Just as an OSI protocol standard must include a clause stating conformance requirements to that protocol, a profile must include a clause stating conformance requirements for the profile.

11.2.3 Principles of Profiles

• A profile restricts the choice of base standard options to the extent necessary to maximize the probability of interworking;
  
• however, it must not specify any requirements that would contradict or cause non-conformance to a base standard;
  
• but it may specify requirements which are more specific than those of the base standard; it might exclude some optional capabilities which are valid in the standard.

In general in a base standard, a particular feature is mandatory, optional, or conditional. If it is mandatory, it must be mandatory in a profile. A feature which is optional or conditional in the base standard could be mandatory, optional, conditional, or excluded in the profile.

11.3 Taxonomy of TC46 ISPS

11.3.1 General Taxonomy of Profiles

• connection oriented transport profiles; (T-profiles)
  
• connectionless transport profiles; (U-profiles)
  
• profiles for relay functions between T profiles or between U profiles; (R-profiles)

For the upper three layers there are:

• application profiles for use with T profiles; (A-profiles)
  
• application profiles for use with U profiles; (B-profiles)
  
• interchange format and representation profiles; (F-profiles)

An SR or ILL profile will fall into the A class, for use with a T-profile.

11.3.2 A-profile Identifiers

For LD, "a" takes the value 1 for pure SR profiles, the value 2 for pure ILL profiles, and the value 3 for profiles where both SR and ILL are included.

11.3.3 ALD Profiles

The taxonomy contains the following profiles:

       PROFILE NAME                                              Identifier
       Library and Documentation Applications                       ALD
       Search and Retrieve (SR)                                     ALD1
       SR, connection-oriented                                      ALD11
       SR, Store-and-Forward (IPMS)                                 ALD12
       Interlibrary Loan (ILL)                                      ALD2
       ILL, connection-oriented                                     ALD21
       ILL, Store-and-Forward (IPMS)                                ALD22

11.4 Short Description of TC46 ISPS

Each ISP for the Library and Documentation sector refers to the generic documents, ALD1 and ALD2.

Two sets of documents have been defined for ISPs for Library and Documentation sector, those relating to SR and those relating to ILL. An ISP may refer to documents in both sets as well as to parts of other profiles.

The following parts have been defined for the ALD ISPs:

• Information and documentation - Open Systems Interconnection (OSI) - International Standardized Profiles ALD1n - Library and Documentation - Search and Retrieve -
  
  Part 1: Specification of ACSE, Presentation and Session Protocols for use by ALDn1
  Part 2: Search and Retrieve Generic for ALD1n
  Part 3: ALD11 Search and Retrieve using Connection-oriented ACSE

• Information and documentation - Open Systems Interconnection (OSI) - International Standardized Profiles ALD2n - Library and Documentation - Interlibrary Loan -
  
  Part 1: Specification of Message Handling System (MHS) for use by ALDn2
  Part 2: Interlibrary Loan Generic for ALD2n
  Part 3: ALD21 Interlibrary Loan using Connection-oriented ACSE
  Part 4: ALD22 Interlibrary Loan using Message Handling Systems