Community Vocabularies Layer

Community Vocabularies Layer

As you’ve probably noticed, we’ve spoken about every part of the XML standards stack except for one: the Community Vocabularies layer. On top of all these various layers and aspects sits the Community Vocabularies layer. This is the layer where all the industry-specific implementations and problem-oriented specifications are created. In effect, this is where the “rubber meets the road.” Community vocabularies, which can be vertical industry specifications and standards or cross-industry specifications, make use of all or some of the aforementioned technologies and specification layers to accomplish their goals.

Community vocabularies specify the actual metadata and information that represents how a given user community plans to make use of XML. These community vocabularies may represent a need in an industry, such as insurance or electronic component manufactur-ing, or a horizontal user community, such as online gaming or data warehousing. In any case, the vocabularies define the specifics of data interchange that can then be repre-sented using Process layer specifications, utilizing Service layer components, packaged into Message layer messages, transmitted over Transport layer protocols, and utilizing any combination of security, presentation, query, and semantics aspects. Thus, the com-munity vocabulary forms the top layer.

Although community vocabularies represent the absolute top of the XML standards stack, they often are some of the first specifications to be developed. The reason for this is quite simple: Some need motivated the desire to implement XML in the

first place! In many cases, this was a desire to communicate between industry partici-pants, such as in the financial services, manufacturing, or healthcare arenas. However, when it came time to implement these specifications, the various specification-writing bodies realized that some of their required pieces of functionality, as represented by the messaging-oriented protocol or document-oriented specification stack, didn’t exist. The result was that industry-specific vocabularies had to define specifications that were of a more general nature. For example, the ACORD specification had many Message layer components defined in its early days. As layers of the XML stack become increasingly more developed, the breadth of individual community vocabulary specifications become increasingly more narrow.

However, while the scope of community vocabularies may be increasingly more focused as other layers of the stack become more developed, the number of community vocabu-laries are proliferating. There’s a vast number of vertical industries and horizontal user communities that desire to define their own, specific XML vocabularies for interchange. In fact, the entire XML standards stack in actuality looks more like an upside-down pyramid when viewed from the perspective of how many different specifications there are in a given level. Whereas there are hundreds, if not thousands, of individual commu-nity vocabulary specifications at the top level, there are very few specifications at the XML Base Architecture layer, and the number increases as we move up the XML specification food chain. One may say that document-oriented specifications remain steady in number, but it can still be argued that the number of document-oriented specifi-cations is greater than the number XML base architecture specifications and less than the number of community vocabulary implementations. Therefore, we have an inverse pyramid of usage, as shown in Figure 19.3, that helps to make our XML standards stack model even more accurate.