Added some information about compilation targets

source/ohuac.rst

@@ -104,3 +104,65 @@ generally **prepended** to the options passed to the subcommand.
 
 Supported targets for code generation
 -------------------------------------
+
+The standalone compiler currently supports two compilation targets. One is a
+universal format, which simply encodes the dataflow graph directly in JSON and a
+second which creates a java class.
+
+.. _code-gen-json:
+
+JSON Graph repesentation
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+The JSON output from ``ohua`` is selected with the ``-g json-graph`` option.
+The default file extension is ``.ohuao``.
+
+This representation only encodes the dataflow graph and the stateful functions
+used. It is intended to be a universal, easily to use intermediate for backeds
+which have no direct support in ``ohuac`` yet. Such a backend only has to define
+the runtime for the dataflow execution and the loading and linking of stateful
+functions, ``ohuac`` will take care of parsing, interpreting and optimising the
+algorithms.
+
+.. _code-gen-simple-java:
+
+A simple runnable java class
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``-g simple-java-class`` code gen option is a very lightweight code
+generation for the java platform.
+
+It generates a class where the module path is its package and the algorithm name
+is the name of the class. E.g. namespace ``foo.bar.baz`` with the ``main``
+algorithm selected generates a class ``foo.bar.baz.Main``.
+
+For an algorithm ``main`` with arguments ``A``, ``B``, ``C`` and return type of ``D``,
+the class has the following structure
+
+.. code-block:: java
+
+   class Main {
+      public static C invoke(A argument0, B argument1, C argument2);
+      public static Configured configure(RuntimeProcessConfiguration configuration);
+
+      public static class Configured {
+          public Prepared prepare(A argument0, B argument1, C argument2);
+      }
+      public static class Prepared {
+          public static D invoke();
+      }
+   }
+
+The argument and return types default to ``Object``.
+
+
+The structure of the class follows a simple schema. Each algorithm class has two
+``static`` methods ``invoke`` and ``configure``. ``invoke`` simply executes the
+algorithm with the default runtime parameters. ``configure`` allows
+customization of runtime parameters.
+
+Furthermore there are always two inner classes, ``Configured`` and ``Prepared``.
+The two inner classes represent stages of algorithm configuration.
+``Configured`` is a graph with an associated runtime configuration and can be
+turned into a ``Prepared`` by calling ``prepare`` with the arguments specified
+in the algorithm description.