Skip to main content

Participants

Today it was the turn of participants to get a hammering.

A SOA is all about people; about people getting things done. What is more, people have all kinds of relationships to each other :-). What, you might ask, has that got to do with SOA? A lot in my opinion.

Here is an example. Suppose that someone wants to set up a system that allows, among other things, groups, teams, and societies (such as the Society for the Preservation of Cats in the San Francisco neighborhood) to be formed and policed. There are many situations where that is already happening, just take a look at MySpace. Well, each society is going to want its own rules for governing itself. Of course, there is always an overarching set of rules that we abide by: the state and federal law; but federal law tries not to interfere too much in the way that the SPCSF is run.

Our SOA that is supporting all these societies might allow people to execute actions via the SOA: such as declaring that someone is the president, a meeting quorate and so on.

What is a service to do when it receives a request to promote a society member the new president of that society? Certainly, we could restrict the system to record keeping, but a deeper system will try to ensure that the promotion is valid. That involves knowing if the promotion action is from a valid source, whether the action is properly enacted and so on.

All of these validations, and the consequences that follow from the action (the new president can call meetings to order) are really about these other 'out of band' relationships between participants in the SOA system.

The same is really also true for ordinary commerce: a minor may not legally enter a contract (and therefore may not legally buy anything over the Internet). Such a fact is currently respected in the breach more than the observance; but I expect that things like SOX will change that for a lot of people. Enterprises are a lot more like mini-societies than most IT staff (and C*Os) give credit for.

We are trying to ensure that our Reference Architecture properly accounts for the possibility of these out of band relationship because they affect the performance of the system itself. Of course, it is not our job to define what the rules are; only how any set of rules might integrate with SOA-style systems.

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…