There are many possible models of deployment that can apply, particularly to products:
- Local deployment & installation, with a private/independent copy at each installed site
- Centralized, shared, monolithic, such as a travel service web site, or even something like Google Docs
- Decentralized and distributed
There are others, too. Each one of these may or may not lend itself well to a particular maintenance and support model:
- Supporting multiple historical versions
- Supporting only current version while working on the next one
- Supporting a product-family of variants of the same set of components
Which model you use depends primarily on upon total number and type of distinct customer-bases and the market (i.e., how likely it is you can expect them to be willing and able to upgrade to new major versions and how much they are willing to pay you to support older ones).
With the above definition, we can review some of the SCM considerations as to the difference between products and projects. We have discussed how many release engineering issues can be addressed through a balance of architecture, organizational approach, and SCM strategy. Also, using the above definitions, we can consider project SCM needs to be a subset of product SCM.
Product development tends to have release lines - potentially multiple independent projects under development at the same time. As Laura Wingerd discusses in Chapter 7 of her O'Reilly Book (Channeling the Flow of Change):
- First, at any point in time there is likely to be more than one supported product version available to customers. Ace must be prepared to field customer calls, diagnose problems, and fix critical bugs in all of their currently supported versions.
- Second, not all development tasks have the same urgency. Some are expected to yield results immediately while others are targeted for distantly future releases.
- Third, software development is not entirely predictable; some projects go according to plan, others get mired in unforeseen difficulties.
Laura presents release and project branching patterns, and also discusses the Mainline branching model.
The ITIL Service View
Many organizations undertake a variety of internal projects that deliver new or enhanced applications or systems into live usage within the organization. A typical new system or product, delivered as part of a project, might follow a lifecycle and branching model shown below.
From an ITIL viewpoint, the service transition phase (e.g. into live usage) is very important and one of the key measurements is the ongoing documentation and support process that allow the system to be cost effectively maintained in the future. This recognizes the reality that the initial development of most systems is 30% or less of the overall lifetime of a syste
As mentioned above, project teams who are measured only with regard to successful delivery of their project and then leave, for the next project, can leave considerable maintenance problems behind them. We have seen this plenty of times as a significant problem for organizations. And yet this model is still very common.