We have a back end that exposes 50-60 Rest APIs. These will largely be consumed by standalone applications like a Python script or a Java program.
One issue we have is the APIs are at a very granular level, they do not match the business use case. For example to perform a business use case end user might have to call 4 to 5 APIs.
I want to develop a DSL or some solution that will help provide a high level abstraction that will enable end users to implement business use cases with ease. This can either be a standalone abstraction or a "library" for Python or or some much high level programming language.
For the specific purpose of combining multiple Rest API calls to create a business use case transaction, what are the approaches available.
Thanks
I think this is a nice idea. To determine what kind of solution you could build you should consider different aspects:

Who would write these API combinations?
What kind of tool support would be appropriate? I mean validation, syntax highlighting, autocompletion, typesystem checks, etc
How much time would make sense to invest on it?

Depending on these answers you could consider different options. The simplest one is to build a DSL using ANTLR. You get a parser, then you build some program to process the AST and generate the code to call the APIs. Your user will just have to edit these programs in a text editor with not support. The benefit of this is that the cost of implementing this is reduced and your user could write these programs using a simple text editor.
Alternatively you could use a Language Workbench like Xtext or Jetbrains MPS to build some specific editors for your language and provide a better editing experience to your users.
Meta language for rest client