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- The details are those things that are necessary to enable humans, other systems, and
- programmers to communicate with the policy, but that do not impact the behavior of
- the policy at all. They include IO devices, databases, web systems, servers,
- frameworks, communication protocols, and so forth.
- The goal of the architect is to create a shape for the system that recognizes policy as
- the most essential element of the system while making the details irrelevant to that
- policy. This allows decisions about those details to be delayed and deferred.
- For example:
- • It is not necessary to choose a database system in the early days of development,
- because the high-level policy should not care which kind of database will be used.
- Indeed, if the architect is careful, the high-level policy will not care if the database
- is relational, distributed, hierarchical, or just plain flat files.
- • It is not necessary to choose a web server early in development, because the high-
- level policy should not know that it is being delivered over the web. If the high-
- level policy is unaware of HTML, AJAX, JSP, JSF, or any of the rest of the
- alphabet soup of web development, then you don’t need to decide which web
- system to use until much later in the project. Indeed, you don’t even have to decide
- if the system will be delivered over the web.
- • It is not necessary to adopt REST early in development, because the high-level
- policy should be agnostic about the interface to the outside world. Nor is it
- necessary to adopt a micro-services framework, or a SOA framework. Again, the
- high-level policy should not care about these things.
- • It is not necessary to adopt a dependency injection framework early in
- development, because the high-level policy should not care how dependencies are
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