Summary: Semistructured data are used to model data transferred on the Web for applications such as e-commerce, biomolecular biology, document management, linguistics, thesauri and ontologies. They are formalized as trees or more generally as (multi-)graphs. Query languages for semistructured data have been proposed that, like SQL, can be seen as involving a number of variables, but, in contrast to SQL, give rise to arrange the variables in trees or graphs reflecting the structure of the semistructured data to be retrieved. Leaving aside the “construct” parts of queries, answers can be formalized as mappings represented as tuples, hence called answer tuples, that assign database nodes to query variables. These answer tuples underly the semistructured data delivered as answers.
For the entire collection see [Zbl 0953.00043].