For the last 6 months I've been investigating the separation of nouns and adjectives from the verbs and adverbs. For those that don't follow my blog on a regular basis, here is a quick summary:
Nouns are people, places and things - in the software world they are our domain entities (User, Invoice, etc.) - and adjectives are the properties that describe the nouns. In the J-world we used Java classes to describe them - in the W-world we use XML schemas.
Verbs are the actions. Actions have (at least) two forms: technical (insert, update, delete, publish, etc.) and domain or business specific (ship, pack, etc.).
Technical verbs often act the same way on any given noun. Why is this important? Imagine walking into an enterprise with a set of nouns on a floppy disk. The company already has a service network in place. This ServiceNet is composed of 12 servers (portal, database, security, etc.) and runs 46 services. Each server has the capability of 'listening for new nouns' and a 'registration service' has the responsibility of: 1. Notifying the servers of newly registered nouns and 2. Notifying the servers of newly registered servers.
Ok, we just moved into a world where the network is aware of the network. No magic, just simple registration. What gets interesting is when nouns have 'default implementations' of a verb on a server. And surprisingly, you will find that this is possible and beneficial. If I add a new noun to the ServiceNet will it likely have security permissions? Will it need to be stored? Will it be viewed? Should I role all of this code by hand? Again, the goal isn't to perform magic - it is to create a network programming model where we think more about how to create smart verbs and dumb nouns. The servers are slowly given the ability to interrogate each other and eventually a common set of functions is factored out of the servers and dropped into the network.
I'm convinced that service oriented programming has the potential to get absolutely unmanageable. I talk with customers every day - they almost always start the conversation by bragging about the number of services that they have. Every time I hear this I think "Oh my God, what a maintenance nightmare! And they've only begun." In Schneider-land, the goal is to go for the smallest number of services, with the highest amount of reuse. Figuring out how to do this is a bitch.
Going from Services to the ServiceNet
The first step that I recommend is to take a look at all of the operations on all of your wsdls. Categorize what you already have (VerbOnly, VerbNoun, VerbMechanism, other). Then, determine if you could have made more re-usable services. What would they look like? Create a spreadsheet with the verbs as rows and the nouns as columns. The cells (or intersection points) are the realization of the VerbNoun. Beware of verb synonyms, or made up verbs (verbs that are really nouns). What is the smallest number of verbs you require to fulfill your needs?
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