+#ifndef Query_H
+#define Query_H
+
+#include <QueryCallbacks.h>
+#include <BindingTable.h>
+#include <Relation.h>
+
+/**
+ * A Query is an implementation of a generic ABI over relations. It's
+ * more or less a "virtual Relation" representing a logical composite
+ * access of actual relations, and as such its active part is held in
+ * a separate \ref Querytype record similar to how \ref ItemKeyFun
+ * records define valye types.
+ */
+typedef struct Query {
+ struct QueryCallbacks *def;
+} Query;
+
+/**
+ * \brief Trampoline for the callback function to reclaim the Query
+ * memory for a given Query.
+ *
+ * \param this is the specific \ref Query concerned.
+ *
+ * Ground queries recalim their own state memory. Composite
+ * queries first propagate the reclaim call to its components, and
+ * thereafter reclaim their local state memory.
+ */
+extern void Query_reclaim(Query *this);
+
+/**
+ * \brief Trampoline for the callback function to update the Binding
+ * table with a succession of alternative bindings.
+ *
+ * \param this is the specific \ref Query concerned.
+ *
+ * \param bt is the Binding table to set bindings in.
+ *
+ * \param s is the call "sub-command" for the function.
+ *
+ * \returns 1 if a new Binding is provided and 0 otherwise.
+ *
+ * This function is called repeatedly for successively obtaining
+ * the alternative bindings that satisfy the Query. The "initial"
+ * state sub-command tells the function to capture the incoming
+ * BindingTable state so that the function can later restore it
+ * upon the "restore" sub-command. Upon the "initial" command, the
+ * function also sets up the Binding table with its first Binding
+ * alternative. This is followed by a series of "subsequent"
+ * sub-command calls for the function to change the BindingTable
+ * for its succession of Binding alternatives. The function should
+ * return 1 after any successful Binding setup, and return 0 when
+ * it cannot setup any (more) Binding.
+ */
+extern int Query_next(Query *this,BindingTable *bt,enum NextState state);
+
+/**
+ * \brief Trampoline for the callback function that adds its binding
+ * names to the hashvector.
+ *
+ * \param this is the query concerned.
+ *
+ * \param hv is the HashVector for collating names.
+ */
+extern void Query_variables(Query *this,HashVector *hv);
+
+
+
+
+/**
+ * \brief Creates an assignment Query.
+ *
+ * \param arity is the assignment tuple arity.
+ *
+ * \param names is the (char*) names to assign.
+ *
+ * \param values is the (void*) values to asign.
+ *
+ * The two tuples must have the same arity for assigning names[i] to
+ * values[i]. This Query makes the given names have the given values,
+ * once for each (*next) call following a (*reset) call.
+ *
+ * \related Query
+ */
+extern Query *Query_assign(int arity,Tuple *names,Tuple *values);
+
+/**
+ * \brief Create a Query record for lookup data in a Relation.
+ *
+ * \param r is the relation being queried.
+ *
+ * \param names is a same-arity tuple of binding names for the
+ * columns, using \b 0 for unnamed columns.
+ *
+ * \param values is a same--arity tuple of query values, using \b 0 for
+ * columns to enumerate.
+ *
+ * The names and values tuples identify bindings and values to use for
+ * the search query, and which bindings to set up from the successive
+ * results. Names that are bound beforhand identify constraining
+ * values, and the names that are unbound gain successive values from
+ * the matching tuples.
+ *
+ * \related Query
+ */
+extern Query *Query_Relation(Relation *r,Tuple *names,Tuple *values);
+
+/**
+ * \brief Create a Query record for a conjunction of queries.
+ *
+ * \param n is the number of sub queries.
+ *
+ * \param ... are the sub queries.
+ *
+ * The conjunction query processes the sub queries in order resulting
+ * in the sequence of their combined bindings.
+ *
+ * \related Query
+ */
+extern Query *Query_and(int n,...);
+
+/**
+ * \brief Create a Query record for a disjunction of queries.
+ *
+ * \param n is the number of sub queries.
+ *
+ * \param ... are the sub queries.
+ *
+ * The disjunction query processed the sub queries in order to find
+ * all their individual "true" binding combinations. It processes one
+ * sub query at a time to exhaustion and provide their individudal
+ * binding sequences separately.
+ *
+ * \related Query
+ */
+extern Query *Query_or(int n,...);
+
+/**
+ * \brief Invoke a consequent callback function for each successful
+ * binding of a query.
+ *
+ * \param q is the antecedent query to process.
+ *
+ * \param bt is the binding table to use.
+ *
+ * \param consequent is the callback function to invoke for each
+ * binding.
+ * \param data is the caller's context data.
+ *
+ * This function prrocesses the Query for establishing its binding
+ * sequence and inokes the consequent callback function for each
+ * binding as it is provided.
+ *
+ * \related Query
+ */
+extern void Query_eval(
+ Query *q,BindingTable *bt,
+ int (*consequent)(BindingTable *bt,void *data),
+ void *data );
+
+/**
+ * \brief Collect all bindings of query.
+ *
+ * \param q is the query to enumerate.
+ *
+ * \param names is the binding names to track.
+ *
+ * \param results is the result store of bindings for the names.
+ *
+ * \returns the number of results.
+ *
+ * This function evaluates the query for one round of bindings, and
+ * stores their value \ref Tuple Tuples in the given vector. The given
+ * vector is first cleared, and any item is reclaimed with \b free.
+ * Correspondingly the binding \ref Tuple Tuples are allocated with \b
+ * malloc for the caller to reclaim (possibly via a successive call to
+ * this function).
+ */
+//extern int Query_snapshot(Query *q,Tuple *names,Vector *v);
+
+/**
+ * \brief Creates an NotQuery.
+ *
+ * \param query is the query to negate.
+ *
+ * \related Query
+ */
+extern Query *Query_not(Query *values);
+
+#endif