Skip to main content

A missing piece

For some time now I have been thinking that the key to a framework for safe and effective action across the Internet was the Norms and Institutions paradigm. In that paradigm, the key concept (it seems to me) was the social act; or rather, that all human actions are rooted in the social context.

At the same time, we have been working on the SOA Reference Architecture, and I feel that it is important that SOA itself be grounded in the N&I paradigm. In the approach that we are taking, we are taking multiple views on the SOA theme. Each view is characterized by a viewpoint -- literally a point of view of the architecture. One of these views is the Service as Business view, and this view is expressed in language that would be instantly familiar to anyone aware of the Norms and Institutions framework.

A challenge in such a multi-layered approach to architecture is to link the different levels together in a convincing way (ideally, in a way that is both clear and obviously supporting).

In this case, one such challenge is in linking the information exchange level of the SOA (e.g., SOAP message exchange) with the business view (e.g., buying a book). It is certainly true that any interpretation of a SOAP message as anything other than a bunch of XML is somehow extraneous to the SOAP message itself. SOAP (and related specs) simply does not have the language or conceptual framework to deal with book buying (say).

Hence the concept of a business transaction. For business types, this is a fundamental idea: we agree that you will ship me the book and I will pay for it. From the business perspective how this agreement is reached is pure IT (and boring).

For us, however, we need to relate a business transaction to an interchange of SOAP. This leads to the concept of supervenience.

One system can be said to supervene over another if (a) the first system uses the second in a replaceable manner (a different message exchange mechanism would do just as well) and (b) the second lower-level system is neutral in respect of the higher-level system. I.e., if the higher-level use is simply one possible application of the lower-level system and could be applied to other uses without fundamentally affecting its functioning.

So, the business transaction 'system' supervenes on the message exchange system quite nicely. Another way of saying this is that business transactions provide an effective way of capturing the meaning of SOAP-level information exchange at a level that is meaningful to people who are not IT geeks.

Popular posts from this blog

Comments Should be Meaningless

This is something of a counterintuitive idea:
Comments should be meaningless
What, I hear you ask, are you talking about? Comments should communicate to the reader! At least that is the received conventional wisdom handed does over the last few centuries (decades at least).

Well, certainly, if you are programming in Assembler, or C, then yes, comments should convey meaning
because the programming language cannot
So, conversely, as a comment on the programming language itself, anytime the programmer feels the imperative to write a meaningful comment it is because the language is not able to convey the intent of the programmer.

I have already noticed that I write far fewer comments in my Java programs than in my C programs.  That is because Java is able to capture more of my meaning and comments would be superfluous.

So, if a language were able to capture all of my intentions, I would never need to write a comment.

Hence the title of this blog.

Existential Types are the flip side of generics

Generic types, as can now be seen in all the major programming languages have a flip side that has yet to be widely appreciated: existential types.

Variables whose types are generic may not be modified within a generic function (or class): they can be kept in variables, they can be passed to other functions (provided they too have been supplied to the generic function), but other than that they are opaque. Again, when a generic function (or class) is used, then the actual type binding for the generic must be provided – although that type may also be generic, in which case the enclosing entity must also be generic.

Existential types are often motivated by modules. A module can be seen to be equivalent to a record with its included functions: except that modules also typically encapsulate types too. Abstract data types are a closely related topic that also naturally connect to existential types (there is an old but still very relevant and readable article on the topic Abstract types have …

Concept Oriented Markup

I have long been frustrated with all the different text mark up languages and word processors that I have used. There are many reasons for this; but the biggest issue is that markups (including very powerful ones like TeX) are not targeted at the kind of stuff I write.

Nowadays, it seems archaic to still be thinking in terms of sections and chapters. The world is linked and that applies to the kind of technical writing that I do.

I believe that the issue is fundamental. A concept like "section" is inherently about the structure of a document. But, what I want to focus on are concepts like "example", "definition", and "function type".

A second problem is that, in a complex environment, the range of documentation that is available to an individual reader is actually composed of multiple sources. Javadoc exemplifies this: an individual library may be documented using Javadoc into a single HTML tree. However, most programmers require access to multiple…