tailieunhanh - Advances in Database Technology- P7

Tham khảo tài liệu 'advances in database technology- p7', công nghệ thông tin, cơ sở dữ liệu phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 282 O. Shmueli G. Mihaila and S. Padmanabhan 5. Step-Predicate Consistency If V maps a Predicate to node u in Td and ip maps the first step of the RLP of the PredExp of the Predicate to node v in Td then u v is an edge in Td. 6. Comparison Mapping ip maps the Op Value part of a predicate self node Op Value to the node it maps the self step and the condition Op Value is satisfied by this node. Similarly to an expression mapping a matching map is also a function from expression components into tree nodes this time nodes of T rather than Td. A matching map satisfies the same six conditions listed above3. As we shall see the existence of an expression mapping function from to implies the existence of a matching map from e to T. Let T be a tagged tree Td an image data tree of T and e a normalized expression. Suppose there exists an element occurrence elem in Td computed by e on Td as evidenced by an expression mapping from e to Td. We associate with a matching map such that if maps a component of to a node in Td then Vv maps c to the node u in T such that v is an image of u. Because of the way images of tagged trees are defined if maps to and to and u v is an edge in Td then p ci ipp c2 is an edge in T. Furthermore the node tests that hold true in Td must be true in T that is Node Names are the same and if text holds on the node then the corresponding T node manufactures text. We also call a matching of and T. Observe that there may be a number of distinct matching maps from the same normalized expression to T. Perhaps the simplest example is a tagged tree T having a root and two children tagged with A . Let e be Root child A we can match the step child A with either of the two A children of the root of T. Observe that these two matching maps correspond to different ways of constructing an expression mapping from to a data tree of T. 4 Tagged Tree Rewriting Rewriting is done as follows Based on a matching map for an expression the tagged tree is modified subsection