Monthly Archives: August 2005

Almost all integration projects contain one or more transformations (sometimes called “mappings”) between two different structures holding equivalent data (for example the order tables in the database, and the order XML message). We know how to model the individual static data structures in various ways, but the most common approach is to represent each by a UML class model, and there are established conventions for how to do this for different data sources.

However, UML doesn’t help when it comes to the transformations themselves, and typically the detail has to be captured either in code, or a proprietary format. Most good integration tools provide some sort of “visual mapping tool”, where the developer drags and drops to create links between representations of the two structures, usually imported directly from their physical schemas. Here’s an example using SeeBeyond. Altova provide a good stand-alone data mapping tool called Mapforce – here’s an example showing it in use. The problem is that these tools work directly with the physical structure, and don’t export the mapping information in a reusable format, so that information is completely disconnected from the UML analysis or design models.

I have experimented with trying to represent mapping information in a UML model, but so far without much success. The best solution I’ve found so far is to use some sort of “pseudo code” (it could be OCL, pseudo-Java, pseudo-VB or anything similar). For example, we could easily annotate the model with code fragments such as:

Database.order_table.order_no = Message.Header.OrderNo

(where each element refers to a UML Package.Class.Attribute combination).

The problems are that it’s not clear where to put this annotation, most UML modelling tools won’t help generate it, and there’s no graphical representation. Ultimately, writing pseudo-code like this is probably not much better than abandoning the model and moving straight to using your integration tool.

My question is: does anybody know a better way? Has anybody found a good way of representing mapping information in UML? And if so, is there any good tool support?

If you know, please send me a message.

There’s been a lot of talk in recent years about a “city planning” metaphor for Enterprise Architecture development. Pat Helland’s article “Metropolis” in the Microsoft Architecture Journal is a very good example (see my post on this for some key quotes).

While the metaphor might still be valid, some people are beginning to question how far it should be taken. Helland’s article, like others before it, implies that “good” EA looks rather like a medium-sized modern American town, complete with relatively standard services, civic buildings and commercial venues. In an answer to the original “Metropolis” article Richard Veryard and Philip Boxer have published “Metropolis and SOA Governance” which challenges several of Helland’s assumptions.

I think that maybe we should extend the metaphor by thinking about cities, or Enterprise Architectures, as very diverse entities. What sort of “city” do you live in? To what extent is it planned? What is the vision, and do the citizens share in it? Does the EA resemble a nice neat midwest town, a dark, brooding Gotham City, a glass and steel Utopia, a federation of small towns with lots of empty space between them, a medieaval walled town, or a wartime mid-european ghetto?

And the metaphor can be taken further. Do you want to promote “infill development”, closing up functional gaps, or do you want to keep clear separation between the various zones? Do you want the shared services to be clearly visible, as they are in modern, purpose-built towns or hidden beneath a facade which looks much older or simpler? Do you expect to eventually knock down and rebuild older “legacy” zones, or do you want to preserve them with the minimum of change (a common requirement for our valuable historic buildings)? Do you want to accomodate the small hardware shop (read small the bespoke system) as well as the new DIY superstore (the ERP package)?

Finally, remember that it is extremely rare for a city to be truly planned and designed from scratch. You usually start with something established. Even if the city has been flattened by a bomb, you’ll have to observe land rights (this is what stopped Christopher Wren and Charles II realising their grand design after the Fire of London). This is equally true of Enterprise Architectures.

The city planning metaphor is a powerful one, but its true power may come if we use it to explore problems as well as utopian ideals.