Allow programs to specify the type of data they can consume and the type of the data they emit. This is how powershell does it (using the dotnet type system).

And the problem is how can you ensure the output type of one program matches the input type of another.

A program emits one type, and the other program accepts another.

Something will be needed to transform one type into another. Imagine doing that on the command line.

Cat file1 | convert | dest