Modeling dependencies into parallelism/serialism. How to?

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How do I take a set of dependencies and model them as a serial and parallel actions?For example:U1 depends upon U2could be a serial representation of\[code\]S: [U1, U2]\[/code\]U1 and U2 are not dependent would be a parallel representation.\[code\]P: [U1, U2]\[/code\]S means serial, and P means parallel. In this example U refers to a URL that points to a resource.In parallel resources the ordering does not matter. In serial resources the ordering does matter.I'm trying to build a resource loader.It only needs to work with the local server. Also, it only uses Ajax get requests to load resources.But I want to a language/syntax to model the complexity of dependent resources.Note:This is for learning/later implementation. No outside libraries unless you can relate the syntax they use for loading to the question.A practical example:Jqueryui depends upon jquery. This would be represented as...\[code\]S: [U-jquery, U-jqueryui]\[/code\]Example 2jquery.js does not depend upon modernizr.js. This would be represented as...\[code\]P: [U-jquery, U-modernizer]\[/code\]