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+#ifndef __Query_h__
+#define __Query_h__
+
+//
+// Query.h
+//
+// Query: (abstract) a parsed, 'executable' digger database query
+// a query tree is formed by leaf objects (ExactWordQuery) and
+// node objects (OperatorQuery) derived from this class.
+// Query execution results are returned as ResultList objects.
+// Query evaluation is cached. Cache policy is delegated to the
+// QueryCache class family.
+//
+// Part of the ht://Dig package <http://www.htdig.org/>
+// Copyright (c) 1995-2004 The ht://Dig Group
+// For copyright details, see the file COPYING in your distribution
+// or the GNU Library General Public License (LGPL) version 2 or later
+// <http://www.gnu.org/copyleft/lgpl.html>
+//
+// $Id: Query.h,v 1.4 2004/05/28 13:15:24 lha Exp $
+//
+
+//
+// for details about the basic architectural patterns see the book:
+// Design Patterns, by the infamous GoF
+// Interpreter pattern
+// Factory pattern
+// Flyweight pattern
+//
+
+#ifdef HAVE_CONFIG_H
+#include "htconfig.h"
+#endif
+
+#include "Object.h"
+#include "htString.h"
+#include "ResultList.h"
+
+class QueryCache;
+
+// abstract
+class Query : public Object
+{
+public:
+ // destr
+ virtual ~Query();
+
+ // does nothing here -- hack for comfortable parser coding
+ virtual void Add(Query *) {}
+
+ // get a boolean-style query string
+ virtual String GetLogicalWords() const = 0;
+
+ // evaluate if necessary and return results
+ ResultList *GetResults();
+
+ // set a cache policy
+ static void SetCache(QueryCache *c) { cache = c; }
+
+protected:
+ // get an unique cache index
+ virtual String GetSignature() const = 0;
+
+ Query() {}
+
+ // generate results
+ virtual ResultList *Evaluate() = 0;
+
+ // by default, nothing -- for use of leaf queries
+ virtual void AdjustWeight(ResultList &) {}
+
+private:
+ // the current cache object, if some
+ static QueryCache *cache;
+};
+
+#endif