Schemas/Readme: more details for each type of configuration file

The scope of this readme is widened to document the hierarchy of configuration
files and details on the content of each of them.

Signed-off-by: David Wagner <david.wagner@intel.com>

1 files changed, 47 insertions, 7 deletions

diff --git a/Schemas/README.md b/Schemas/README.md
index 7d9f10d..5d04fad 100644
--- a/Schemas/README.md
+++ b/Schemas/README.md
@@ -12,37 +12,77 @@ Only `ParameterFrameworkConfiguration.xsd`, `SystemClass.xsd`, `Subsystem.xsd` a
 `ConfigurableDomains.xsd` are relevant for use with xmllint: the others are
 included by these 4 XSDs.
 
-You may refer to samples at
-<https://github.com/01org/parameter-framework-samples>.
+**You may refer to samples at
+<https://github.com/01org/parameter-framework-samples>.**
 
 ## ParameterFrameworkConfiguration.xsd
 
-Schema for the top-level configuration.  It contains:
+Schema for the **top-level configuration**.  It contains:
 
 - A reference to the `SystemClass` (aka StructureDescription) XML file (see
   below);
-- The list of plugins to be used;
+- The list of plugins (libraries) to be used. They may be split according to
+the folder they reside in. The `Folder` attribute can either be:
+    
+    - an absolute path,
+    - a relative path (relative to the execution directory),
+    - empty.
+    
+    In the first two cases, the runtime loader will be asked to explicitely load
+    the libraries found in the specified folder; in the last case (empty string)
+    the runtime loader will search for the library on its own (e.g. on Linux
+    distribution this is usually `/lib`, `/usr/lib` - see `man ld.so`)
 - Optionally, a reference to the `Settings`.
 
 Attributes of `ParameterFrameworkConfiguration` are:
 
 - The `SystemClass` name (for consistency check)
-- The `TuningAllowed` (whether the parameter-framework listens for commands)
+- `TuningAllowed` (whether the parameter-framework listens for commands)
 - The `ServerPort` on which the parameter-framework listens if
   `TuningAllowed=true`.
 
 ## SystemClass.xsd
 
-Schema for the SystemClass associated with the top-level configuration.  It
+Schema for the **SystemClass associated with the top-level configuration**.  It
 points to all the "Subsystem" files (see below).
 
+The `Name` attribute of the SystemClass must match the `SystemClass` attribute
+of the top-level configuration file. This name will be the first component of
+all parameters in it, i.e. if its name is "FooBar", its path is `/FooBar`. We
+will use this name in examples below.
+
 ## Subsystem.xsd
 
-Schema for all Subsystem files (aka Structure files).  These files describe the
+Schema for all **Subsystem files** (aka Structure files).  These files describe the
 content and structure of the system to be managed by the parameter-framework
 and also indicate which plugin is to be used.
 
+A Subsystem has the following attribute:
+
+- `Name` (self-explanatory); again it is the base component of all parameters
+  inside it; i.e. if its name is "Spam", its path is `/FooBar/Spam`;
+- `Type`, which indicates which SubsystemBuilder is to be used (each plugin can
+  declare one or more SubsystemBuilders); it may be defined as `Virtual`, in
+  which case, no plugin will be used and the parameters won't be synchronized.
+  This is useful for debugging but may also be used for the parameter-framework
+  to act as a configurable settings database;
+- `Endianness`: `Little` or `Big`;
+- `Mapping` (optional), defines a Mapping to be inherited by all Components in
+  the Subsystem.
+
+A Subsystem *must* contain:
+
+- A `ComponentLibrary`, which may include (using `<xi:include href="xyz.xml"/>`)
+  other files containing a `<ComponentLibrary>` or a `<ComponentTypeSet>` tag.
+- An `InstanceDefinition` which instantiates the parameters and may use
+  ComponentTypes defined in the ComponentLibrary.
+
 ## ConfigurableDomains.xsd
 
 Schema for the ConfigurableDomains (aka Settings files).  These files contain
 the rules for applying values to parameters.
+
+Writing this file by hand is painful but it is not intended to be dealt
+with directly: instead, you may use the command-line interface (see
+`remote-process/README.md`) to set the settings and export the resulting
+Settings with the `getDomainsWithSettingsXML` command.