Update README.md

Author: marqh

README.md

@@ -2,7 +2,41 @@
 
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-A Python library for validating and managing binary array linked data files.
+A Python library for managing binary array linked data files.
+
+
+## Parsing
+
+This library processes payloads of various encodings and produces metadata graphs, in RDF, of the contents.  
+
+Input payloads are provided with an identity, elements within the payload are identified, with respect to that payload identity, unless they are otherwise identified, by prefix or by alias.
+
+Only Object values (attribute values) may be literals, consistent with the RDF interpretation. All Subjects and Predicates are identified with URIs. 
+
+Some format specific implementation exists, due to the different capabilities available from different encodings.
+
+### netCDF
+
+For netCDF files, no variable to variable reference definitions are provided by the API.
+
+For a variable to variable reference to be interpreted, an externally provided alias or predicate graph must explicitly state that a particular attribute has an rdfs:range of http://binary-array-ld.net/latest/Subject or a subclass of that class.
+
+netCDF parsing is working to support the emerging draft Open Geospaatial Consortium approach to netCDF-Linked-Data: https://github.com/opengeospatial/netCDF-Classic-LD/
+
+### HDF
+
+HDF files and APIs have an object reference, indicating a reference from one element in the file to another.
+
+These object refernces shall always be interpreted as references, regardless of the semantics of predicates (attribute names) provided by external graphs.
+
+
+## Validation
+
+This library provides some limited validation capabilities.
+
+It is expected that a valid input payload will be able to be processed into a graph.  
+
+Validation rules are limited in this implementation to require that provided HTTP URIs resolve.
 
 ## Pre-requisites