Vertically Acyclic Conjunctive Queries over Trees
نویسندگان
چکیده
Seeking a manageable subclass of conjunctive queries over trees that would reach beyond tree patterns, we find that vertical acyclicity of queries is sufficient to guarantee the same complexity bounds for static analysis problems, as those enjoyed by tree patterns.
منابع مشابه
Constant Delay Enumeration for Acyclic Conjunctive Queries over X Structures
We present an efficient answer enumeration algorithm for an extension of Conditional XPath with variables, which is a first-order complete query language for unranked trees of bounded depth. Our algorithm requires constant delay and linear preprocessing time for fixed queries, while depending linearly on the size of the query. It is based on a new enumeration algorithm for disjunctions of acycl...
متن کاملBetween Tree Patterns and Conjunctive Queries: Is There Tractability beyond Acyclicity?
In static analysis of queries over trees in the presence of schemas, there is an exponential complexity gap between conjunctive queries (CQs, positive existential first-order formulae without disjunction) and tree patterns (tree-like acyclic CQs). Motivated by applications in XML data management, we consider various restrictions of CQs that bring their complexity down to that of tree patterns. ...
متن کاملOn the Hardness of Learning Acyclic Conjunctive Queries
A conjunctive query problem in relational database theory is a problem to determine whether or not a tuple belongs to the answer of a conjunctive query over a database. Here, a tuple and a conjunctive query are regarded as a ground atom and a nonrecursive function-free definite clause, respectively. While the conjunctive query problem is NP-complete in general, it becomes efficiently solvable i...
متن کاملPrediction-hardness of acyclic conjunctive queries
A conjunctive query problem is a problem to determine whether or not a tuple belongs to the answer of a conjunctive query over a database. Here, a tuple, a conjunctive query and a database in relational database theory are regarded as a ground atom, a nonrecursive function-free definite clause and a finite set of ground atoms, respectively, in inductive logic programming terminology. An acyclic...
متن کاملEfficient Enumeration for Conjunctive Queries over X-underbar Structures
We investigate efficient enumeration algorithms for conjunctive queries for databases over binary relations that satisfy the X property. Tree-like relations such as XPath axes or grids are natural examples of such relations. We first show that the result of an n-ary conjunctive query Q over an X structure S can be enumerated with a delay in O(n·|S|·|Q|) between two consecutive n-tuples. Then, w...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 2016