15. An apparatus for adaptively evaluating a query with respect to a document that is expressed in a nested-structure, document-specific markup language, the apparatus comprising: a processor; a memory to store computer program instructions, the computer program instructions when executed on the processor cause the processor to perform operations comprising: receiving an original query that is expressed as a tree having a degree d≧3, the tree including query nodes and links that define relationships among the query nodes as being parents, children, ancestors or descendants of each other; relaxing the original query to form a relaxed query; calculating scores for respective candidate answers that include one of partial answers and final answers, the candidate answers including a complete answer to the relaxed query and satisfying all requirements of the relaxed query but satisfying less than all requirements of the original query, a score including: a first portion determined by how many children or descendants a first node has, that are at a given level beneath the first node and that satisfy a first query requirement for that given level; and a second portion determined by what fraction of all a second node's children or descendants at a predetermined level, satisfy a second query requirement for that second node; and applying the scores to govern a processing order of the candidate answers to arrive at an evaluation of the query wherein the score is directly proportional to a mathematical product of the first portion and the second portion, the candidate answers include fragments of the document that are less than the entire document, and a next candidate answer to process from among the candidate answers is chosen by selecting an answer with a maximum possible next score, the maximum possible next score determined by adding a current score of the answer to a maximum possible score the answer could receive from its current server; the calculating further comprising: calculating scores for respective candidate answers comprises calculating scores of progressively smaller fragments of the query that are matched by a candidate answer to be correspondingly smaller scores.
15. An apparatus for adaptively evaluating a query with respect to a document that is expressed in a nested-structure, document-specific markup language, the apparatus comprising: a processor; a memory to store computer program instructions, the computer program instructions when executed on the processor cause the processor to perform operations comprising: receiving an original query that is expressed as a tree having a degree d≧3, the tree including query nodes and links that define relationships among the query nodes as being parents, children, ancestors or descendants of each other; relaxing the original query to form a relaxed query; calculating scores for respective candidate answers that include one of partial answers and final answers, the candidate answers including a complete answer to the relaxed query and satisfying all requirements of the relaxed query but satisfying less than all requirements of the original query, a score including: a first portion determined by how many children or descendants a first node has, that are at a given level beneath the first node and that satisfy a first query requirement for that given level; and a second portion determined by what fraction of all a second node's children or descendants at a predetermined level, satisfy a second query requirement for that second node; and applying the scores to govern a processing order of the candidate answers to arrive at an evaluation of the query wherein the score is directly proportional to a mathematical product of the first portion and the second portion, the candidate answers include fragments of the document that are less than the entire document, and a next candidate answer to process from among the candidate answers is chosen by selecting an answer with a maximum possible next score, the maximum possible next score determined by adding a current score of the answer to a maximum possible score the answer could receive from its current server; the calculating further comprising: calculating scores for respective candidate answers comprises calculating scores of progressively smaller fragments of the query that are matched by a candidate answer to be correspondingly smaller scores. 19. The apparatus of claim 15 , wherein the original query is expressed as an original query tree, the relaxed query is expressed as a relaxed query tree, the relaxing includes removing from the original query, a requirement, in a relationship between an ancestor node and a descendant node, that an intermediate node between the ancestor node and the descendant node be included in the relationship, and relaxing includes preserving a shape of the original query tree while forming the relaxed query tree to have no more nodes than the original query tree.