+1. Starting with data is a data/object-oriented approach, not an SO approach. Data is important most certainly, but in SO the service is king and that's where one should start. The inputs/outputs are driven by desired capabilities of the service, not the other way around. Identify the services first, then define the data formats and semantics.
Haven't we had several "data first" approaches in the past? SQL was going to be the savior of the data-starved business person. OO (data with behavior) was finally going to deliver the agility craved by enterprises. Integration still predominantly focuses on replicating data. The desire for data first is understandable I suppose. We have a long history of "I just need that customer data" or "we need to send the order data over to system X". This is still the predominant "requirement" for most IT projects it seems. "Get that data from there over to there." But SO is supposed to be different. There is data involved but the focus isn't on just moving it around. The focus is on "what do you need to do?" In an SO approach, the answer cannot be "I need to get the customer data." Data access is not a "capability." An SO approach will redirect such "requirements": A: "We need the customer data from system X." B: "Okay, what are you going to do with it? What led you to the conclusion that you need customer data from system X?" A: "Well we're doing this marketing campaign. We're sending direct mailers to customers matching various demographics. We need system X customer data to do that." IMO, even when folks say that they need access to data, they will have started out with some "service", action or capability in mind. They want to do something. They don't want the data just because it's there. IMO, a data first approach undermines SO rather than promotes. -Rob --- In [email protected], "Steve Jones" <[EMAIL PROTECTED]> wrote: > > This is where I disagree. You need to know the capabilities and the > services first in order to the concern yourself with the data inputs > and outputs. I completely agree that the definition of data formats > is important and that interfaces should be designed to be consumer, > rather than producer, friendly. Dave says below that people are > getting it wrong by starting with "services or processes". Maybe a > data centric view doesn't lead to Single canonical form, but it has > done when I've seen organisations take this approach. > > If you aren't starting with the services how can it be service > oriented? Surely that would be a Data Oriented Architecture? > > To know where data is appropriate you have to understand the > services and the capabilities. There are certain data reporting > elements (post transactional) where unified views make sense and > its important to understand those as well, but the important bit is > to first understand the services. I'm not saying data isn't > important but that a view that says "start with the data, then work > up to the services, then the agile layer" implies that services sit > between a data view and a process view, something that only makes > sense in a technically oriented, rather than business oriented, > view of SOA. > > Data is important and you need to understand it, but starting with > it? > > Steve
