Put simply, Clearcase's dynamic views (effectively the developer's sandbox) are implemented with a virtual filing system called MVFS. Files and directories appearing in MVFS are in fact objects from the repository database selected according to a set of rules (the config-spec) - for instance labeled versions, named branches etc.

Dynamic views give rise to another powerful tool: Build auditing. Clearcase associates with each target of a build a complete 'bill-of-materials' used in it's creation. If you're smart, you put the build tools under clearcase too and guarantee to get the exact same versions when you go and revisit a build (for instance when you need to bugfix).