Refine the doc skeleton in the Basic Concept part

Since it has been discussed with Victor, I check it in directly

source/guides/admin-guides/basic_concepts/network_planning/network_service/index.rst

@@ -1,2 +1,2 @@
-Network Services which are used in xCAT
-==================================
+Network Services
+================

source/guides/admin-guides/basic_concepts/xcat_db/index.rst

@@ -1,11 +1,20 @@
-xCAT Database
-=============
+Database
+========
 
-Definition of xCAT DB
----------------------
+xCAT stores all the persistent data used to manage clusters in a database. 
 
-How to Manipulate xCAT DB
--------------------------
+As the administrator, you can use a set of table oriented commands to modify the data (**recommended**), or directly modify the table using the ``tabedit`` command.
 
-How to Use Regular Expression in xCAT DB
-----------------------------------------
+For a more indepth overview see the manpage for xcatdb: ``man xcatdb``
+
+Commands
+--------
+
+Object Definitions
+------------------
+
+Node Groups
+-----------
+
+Regular Expressions
+-------------------

source/guides/admin-guides/basic_concepts/xcat_object/group.rst

@@ -0,0 +1,2 @@
+``group``
+=========

source/guides/admin-guides/basic_concepts/xcat_object/index.rst

@@ -1,12 +1,9 @@
-xCAT Object
-===========
+Objects
+=======
 
-Node Object
------------
-Node Range
+.. toctree::
+   :maxdepth: 2
 
-OSimage Object
---------------
-
-Group Object
-------------
+   node.rst
+   osimage.rst
+   group.rst 

source/guides/admin-guides/basic_concepts/xcat_object/node.rst

@@ -0,0 +1,5 @@
+``node``
+========
+
+Node Range
+----------

source/guides/admin-guides/basic_concepts/xcat_object/osimage.rst

@@ -0,0 +1,2 @@
+``osimage``
+===========