Updated overview section

Update #110

doc/source/images/CMakeLists.txt

@@ -3,6 +3,9 @@ set(IMAGES attribute_manager_uml.png
            hyperslab_uml.png
            property_lists_uml.png
            selection_classes.png
+           hdf5_attributes.svg
+           hdf5_basic_tree.svg
+           hdf5_links.svg
            )
 
 add_sphinx_source(${IMAGES})

doc/source/users_guide/overview.rst

@@ -17,6 +17,44 @@ concepts behind *h5cpp*.
 A high level view on HDF5
 =========================
 
+An HDF5 tree can be considered a tree of objects connected by links. 
+
+.. figure:: ../images/hdf5_basic_tree.svg
+   :align: center
+   :width: 75%
+
+From a very high level point of view we can assume that there are two kind 
+of objects 
+
+1. container objects which can store links to other object 
+2. leafe like objects which cannot hold links to other objects
+
+There is only one container type, a *Group*. For the leaf type of objects there
+are only two: *Datasets* and *commited Datatypes*. We can collect all theses
+objects under one master term: a *node*. From that point of view an HDF5 file 
+is a tree of nodes connected by links. 
+
+In addition each node can be augumented with attributes which can store 
+additional metadata about an objects
+
+.. figure:: ../images/hdf5_attributes.svg
+   :align: center
+   :width: 75%
+
+Attributes can be accessed via their name. Lets have a closer look on the 
+links. 
+
+.. figure:: ../images/hdf5_links.svg
+   :align: center
+   :width: 75%
+
+There are actually three kinds of links connecting objects within a file 
+
+* *hard links* which are created when a new object is created in a file
+* *soft links* which can be used liks symbolic links on a file system to 
+  provide alternative means of access to an object
+* *external links* providing a means to reference objects from a different 
+  file.
 
 
 Nodes and links