Query language requirements

• at least one XML syntax; at least one human-readable syntax.
• must be declarative;
• must be protocol independent;
• must respect XML data model;
• must be namespace aware;
• must coordinate with XML Schema;
• must work even if schemas are unavailable;
• must support simple and complex datatypes;
• must support universal and existential quantifiers;
• must support operations on hierarchy and sequence of document structures;
• must combine information from multiple documents;
• must support aggregation;
• must be able to transform and to create XML structures;
• must be able to traverse ID references.