Weekly Review: The Language of Web Services

Before the advent of telephony, routine long-distance business communications had to take place by overnight mail. The effect on business of substituting the instantaneous direct communication of the telephone call was nothing short of revolutionary.

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Web services promises to have the same revolutionary effect on communications between separate applications, replacing long-winded manual integration processes with instantaneous, platform-independent messaging. But there's a catch. When business people first started talking long-distance by phone, they were able to converse because they all spoke the same language. There's no guarantee applications that direct-dial each other using Web services will share any common language at all.

The Communications Gap
That lack of a common language is the target of initiatives such as the Universal Business Language (UBL), released in a first draft last week by the OASIS standards body (see E-Commerce Standard Plans Made Public). But UBL is just one proposal in a field already littered with many de facto proprietary dialects. Getting all those applications into meaningful conversations with each other is going to be a tough challenge.

At least XML provides a starting point for meeting that challenge. But XML is not the lingua franca of Web services that many suppose it to be. Although the initials stand for eXtensible Markup Language, it's not a language in the sense that English, Russian and Mandarin are languages. It's just a syntax — a set of rules for language. In the same way that all humans are born with a gift for language that allows them to learn whatever tongue is spoken by those around them as they grow up, so XML bestows the gift of language on computer applications, without in any way predisposing them to any given tongue or dialect.

In order to meaningfully exchange information, applications need to add a common language and a shared set of meanings on top of Web services and XML. Conventional application integration fudges this step. It depends on knowing in advance all the phrases that might crop up, and having a transformation table that translates them from one application's private dialect to the other. This has exactly the same benefits and drawbacks as using a tourist phrasebook to get by in a foreign language. It shortcuts the process of actually having to learn the foreign language, but it only copes with known situations. At the first hint of the unexpected, it falls down.

Speaking the Same Language
To achieve the adaptability that is seen as one of the primary benefits of moving to Web services, applications need to be speaking a common language. This is one reason — probably much more of a reason than security worries — why most Web services implementations seem to be between internal enterprise applications: it's much easier to impose a common language when you control both sides of the conversation.

Adopting a neutral language from a third party is another option, and this is where schemas like UBL come in. But UBL may turn out to be too much the computer equivalent of Esperanto, the international language created at the end of the nineteenth century as a culturally neutral means of human communication, and which remains the preserve of enthusiasts rather than a medium for commerce.

The final outcome is much more likely to emulate the real world, in which a handful of de facto languages become dominant, and participating will be a matter of becoming multilingual in those languages. Although UBL and other offshoots of the ebXML initiative from OASIS are in the running, proprietary XML schema from the likes of Microsoft, Siebel, SAP and various vertical industry players are just as likely to win through.

The good news is that XML is designed to allow applications to work in a multilingual environment with much greater facility than humans. Each proprietary XML schema is obliged to publish an XML Schema Definition (XSD), and the theory is that, by comparing an XML document to its governing XSD, an application should be able to adapt to any changes as they occur.

A Matter of Semantics
Unfortunately, that still leaves the nagging issue of what linguists call semantics. Just knowing what a word means in a foreign language doesn't necessarily imply that you understand the sense in which it's being used in any given context. Is a purchase order a binding commitment or merely an intention to purchase? Is a price non-negotiable or does it normally have a service charge attached to it? Such misunderstandings often occur when humans converse by phone without sharing a common cultural or semantic awareness. Allowing applications to converse via XML on our behalf without first establishing a shared understanding runs the risk of incurring similar lapses in communication.

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