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+# module uripattern
+
+by Samer Abdallah, UCL, 2014
+
+
+This directory contains several alternative implementations of a small URI grammar
+which supports both generation and parsing (pattern-matching) of URIs.
+
+There are two variants of the language. The earlier design is quite flexible but
+leads to heavily non-deterministic parsing, which is perhaps not what one wants
+for URI computations which might potentially be called very frequently. The later
+design reduces or eliminates this non-determinism, depending on the implementatation.
+
+### Grammar
+
+We describe the pattern grammar in terms of an algebraic datatype for the pattern language.
+
+
+	uri_pattern ---> prefix:uri_part
+	               ; uri_part.
+
+	P :: prefix :- rdf_current_prefix(P). % any registered prefix atom
+	M :: macro_invocation :- uripattern:def(M,_).
+
+	uri_part ---> \macro_invocation
+	            ; uri_part/uri_part   % slash separated concatenation
+					; uri_part+uri_part   % direct concatenation
+				   ; num(number)         % decimal repn of number
+					; enc(atomic)         % HTML form-encoded atom
+					; atm(atomic)         % any atomic value
+					; <any ground atom>
+					.
+
+The more deterministic grammar removes direct concatenation and arbitrary atom parsing
+but adds a tail/1 functor to capture all the remaining characters in the URI:
+
+	uri_part ---> \macro_invocation
+	            ; uri_part/uri_part   % slash separated concatenation
+				   ; num(number)         % decimal repn of number
+					; enc(atomic)         % HTML form-encoded atom
+					; tail(atomic)        % matches rest of URI
+					; <any ground atom>
+					.
+
+This grammar as written is not quite strict enough to enforce the rule that any tail/1
+term must be the last thing in the pattern. The implementations are slightly less strict
+than this this specification.
+
+
+### Example
+
+Given the following declarations:
+	
+	:- rdf_register_prefix(eg,'http://wwww.example.org/').
+	uripattern:def(matrix(X,Y),num(X)/num(Y)).
+
+Then URIs can be generated as follows:
+
+	pattern_uri(eg:home,A).
+			~> A='http://www.example.org/home'
+	pattern_uri(eg:files/tail('home/chomsky/.profile'),A).
+			~> A='http://www.example.org/files/home/chomsky/.profile'
+	pattern_uri(eg:people/enc('Chomsky, N')/pets,A).   
+			~> A='http://www.example.org/people/Chomsky%2c%20N/pets'
+	pattern_uri(eg:chessboard/matrix(3,6),A).
+			~> A='http://www.example.org/chessboard/3/6'
+
+URIs can also be parsed, eg as follows
+
+	pattern_uri(eg:files/tail(Path),       'http://www.example.org/files/home/chomsky/.profile').
+			~> Path=
+	pattern_uri(eg:people/enc(Name)/pets,  'http://www.example.org/people/Chomsky%2c%20N/pets').
+			~> Name='Chomsky, N'
+	pattern_uri(eg:chessboard/matrix(X,Y), 'http://www.example.org/chessboard/3/6').
+			~> X=3, Y=6
+
+
+### Implementations
+
+There are several implementations:
+
+uripattern\_constraint : Works by splicing atoms and uses delayed goals to handle arbitrary modes.
+
+uripattern\_string : Works by splicing strings.
+
+uripattern\_atom : Works by splicing atoms.
+
+uripattern\_dcg :	Converts URI to and from a list of codes and uses a DCG.
+
+uripattern\_detdcg : A more deterministic DCG
+
+uripattern\_detstring : A more deterministic version of string splicing.
+
+