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README.md

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 # HDF4CPP
 
-TODO: Fill this out later
+## Introduction
+
+The HDF4CPP library is a wrapper library of the hdf4 C interfaces.
+The target was to create a common c++ api to read and write hdf scientific data.
+The only supports the reading of the data at the moment.
+
+## Api overview
+
+### The idea
+
+The idea is to use objects and their methods to do the operations.
+These classes are representing different kind of data,
+so the operation functions are separated. 
+It is easy to decide which object's method I have to call.
+
+### Classes and objects
+
+**HdfObject**       - the base class of all the classes
+
+**HdfFile**         - represents an hdf file
+
+**HdfItem**         - represents an item (SData, VGroup, VData)
+                    - you can get from a file, calling its get function
+**HdfAttribute**    - represents an attribute of an item or of a file
+                    - you can get from a file or from an item, calling its getAttribute function
+
+## How does it work?
+
+### Open an file
+
+```cpp
+hdf4cpp::HdfFile file("/path/to/the/file");
+```
+
+### Get an item, an attribute
+
+```cpp
+hdf4cpp::HdfAttribute fileAttr = file.getAttribute("file attribute name");
+hdf4cpp::HdfItem item = file.get("item name");
+hdf4cpp::HdfAttribute itemAttr = item.getAttribute("item attribute name");
+```
+
+### Get all the items with a specific name
+
+```cpp
+std::vector<hdf4cpp::HdfItem> items = file.getAll("items name");
+```
+
+### Object type
+
+Every kind of hdf data (SData, Vgroup, Vdata) stores different structures.
+These information must be read in a different way, we have to call different methods.
+
+So we get the type of the object just to be sure that we want to read the data in a correct way.
+
+```cpp
+switch(item.getType()) {
+    case hdf4cpp::SDATA:
+        // reading the sdata
+    case hdf4cpp::VDATA:
+        // reading the vdata
+    default:
+        std::cerr << "data is not readable";
+        // note: VGroup has no data to be read
+}
+```
+
+### Reading the data
+
+The **HdfItem** objects have a read function but overridden
+for every reading procedure. 
+The first parameter is a vector in every case, 
+in which the data will be stored.
+
+Check example codes for data specific read instructions.
+
+Note: The library does a type size check, and throws exception 
+in case of missmatch.
+
+### Reading attribute data
+
+Reading attribute data is much more easier than reading the item's data.
+That's because all the attribute data has an array structure.
+The **HdfAttribute** objects have a read function which receives a vector reference.
+Here will be the data stored.
+
+Note: The library does a type size check, and throws exception 
+in case of missmatch.
+
+## Exception mechanism
+
+The library throws **HdfException**.
+This specific exception has **getType** and **getClassType** methods, 
+just to get information about the thrower object.
+Has a **getExceptionType** which returns information about the type
+of the exception, and a **getMessage** method which returns a message
+as string.