job configuration file - the beginning

Rewritten-docs.md

@@ -972,9 +972,45 @@ HTTP(S).
 
 ![Communication schema](https://github.com/ReCodEx/wiki/raw/master/images/Backend_Connections.png)
 
-### Job Configuration
+### Job Configuration File
-
+
-@todo: link to execution unit executed by recodex and lets give this chapter a bit of petite description
+As discussed previously in 'Evaluation Unit Executed by ReCodEx' evaluation unit
+will have form of job which will contain small tasks representing one piece of
+work executed by worker. This implies jobs have to be somehow given from
+frontend to backend. The best option for this is to use some kind of
+configuration file which will represent particular jobs. Mentioned configuration
+file should be specified in frontend and in backend, namely worker, will be
+parsed and executed.
+
+There are many formats which can be used for configuration representation. The
+ones which make sense are:
+
+- *XML* -- is broadly used general markup language which is flavoured with DTD
+  definition which can express and check XML file structure, so it does not have
+  to be checked within application. But XML with its tags can be sometimes quite
+  'chatty' and extensive which does not have to be desirable. And overally XML
+  with all its features and properties can be a bit heavy-weight.
+- *JSON* -- is notation which was developed to represent javascript objects. As
+  such it is quite simple, there can be expressed only: key-value structures,
+  arrays and primitive values. Structure and hierarchy of data is solved by
+  braces and brackets.
+- *INI* -- is very simple configuration format which is able to represents only
+  key-value structures which can be grouped into sections. Which is not enough
+  to represent job and its tasks hierarchy.
+- *YAML* -- format which is very similar to JSON with its capabilities. But with
+  small difference in structure and hirarchy of configuration which is solved
+  not with braces but with indentation. This means that YAML is easily readable
+  by both human and machine.
+- *specific format* -- newly created format used just for job configuration.
+  Obvious drawback is non-existing parsers which would have to be written from
+  scratch.
+
+Given previous list of different formats we decided to use YAML. There are
+existing parsers for most of the programming languages and it is easy enough to
+learn and understand. Another choice which make sense is JSON but at the end
+YAML seemed to be better.
+
+#### Configuration File Content
 
 @todo: discuss what should be in configuration: limits, dependencies, priorities... whatever
 
@@ -1021,9 +1057,6 @@ This format was used because of special dollar sign character which cannot be
 used within paths of regular filesystems. Braces are there only to border
 textual description of variable.
 
-Variables as such will solve problem with specific worker environment and most
-notably specific hierarchy of directories.
-
 ### Broker
 
 The broker is responsible for keeping track of available workers and