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Worst-case Optimal Join Algorithm
A worst-case optimal join algorithm is an algorithm for computing relational joins with a runtime that is bounded by the worst-case output size of the join. Traditional ''binary join'' algorithms such as hash join The hash join is an example of a join algorithm and is used in the implementation of a relational database management system. All variants of hash join algorithms involve building hash tables from the tuples of one or both of the joined relations ... operate over two relations at a time; joins between more than two relations are implemented by repeatedly applying binary joins. Worst-case optimal join algorithms are asymptotically faster in worst case than any join algorithm based on such iterated binary joins. The first worst-case optimal join algorithm, ''generic join'', was published in 2012. Worst-case optimal join algorithms have been implemented in commercial database systems, including the LogicBlox system. Worst-case optimal joins have been applied to build a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comparison Of Join Algorithms
Comparison or comparing is the act of evaluating two or more things by determining the relevant, comparable characteristics of each thing, and then determining which characteristics of each are similar to the other, which are different, and to what degree. Where characteristics are different, the differences may then be evaluated to determine which thing is best suited for a particular purpose. The description of similarities and differences found between the two things is also called a comparison. Comparison can take many distinct forms, varying by field: To compare things, they must have characteristics that are similar enough in relevant ways to merit comparison. If two things are too different to compare in a useful way, an attempt to compare them is colloquially referred to in English as "comparing apples and oranges." Comparison is widely used in society, in science and the arts. General usage Comparison is a natural activity, which even animals engage in when decidin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Algorithm
In mathematics and computer science, an algorithm () is a finite sequence of Rigour#Mathematics, mathematically rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algorithms are used as specifications for performing calculations and data processing. More advanced algorithms can use Conditional (computer programming), conditionals to divert the code execution through various routes (referred to as automated decision-making) and deduce valid inferences (referred to as automated reasoning). In contrast, a Heuristic (computer science), heuristic is an approach to solving problems without well-defined correct or optimal results.David A. Grossman, Ophir Frieder, ''Information Retrieval: Algorithms and Heuristics'', 2nd edition, 2004, For example, although social media recommender systems are commonly called "algorithms", they actually rely on heuristics as there is no truly "correct" recommendation. As an e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Join (SQL)
A join clause in the Structured Query Language (SQL) combines column (database), columns from one or more table (database), tables into a new table. The operation corresponds to a Join (relational algebra), join operation in relational algebra. Informally, a join stitches two tables and puts on the same row records with matching fields : INNER, LEFT OUTER, RIGHT OUTER, FULL OUTER and CROSS. Example tables To explain join types, the rest of this article uses the following tables: Department.DepartmentID is the primary key of the Department table, whereas Employee.DepartmentID is a foreign key. Note that in Employee, "Williams" has not yet been assigned to a department. Also, no employees have been assigned to the "Marketing" department. These are the SQL statements to create the above tables: CREATE TABLE department( DepartmentID INT PRIMARY KEY NOT NULL, DepartmentName VARCHAR(20) ); CREATE TABLE employee ( LastName VARCHAR(20), DepartmentID INT REFERENCE ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Worst-case Complexity
In computer science (specifically computational complexity theory), the worst-case complexity measures the resources (e.g. running time, memory) that an algorithm requires given an input of arbitrary size (commonly denoted as in asymptotic notation). It gives an upper bound on the resources required by the algorithm. In the case of running time, the worst-case time complexity indicates the longest running time performed by an algorithm given ''any'' input of size , and thus guarantees that the algorithm will finish in the indicated period of time. The order of growth (e.g. linear, logarithmic) of the worst-case complexity is commonly used to compare the efficiency of two algorithms. The worst-case complexity of an algorithm should be contrasted with its average-case complexity, which is an average measure of the amount of resources the algorithm uses on a random input. Definition Given a model of computation and an algorithm \mathsf that halts on each input s, the mapping ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hash Join
The hash join is an example of a join algorithm and is used in the implementation of a relational database management system. All variants of hash join algorithms involve building hash tables from the tuples of one or both of the joined relations, and subsequently probing those tables so that only tuples with the same hash code need to be compared for equality in equijoins. Hash joins are typically more efficient than nested loops joins, except when the probe side of the join is very small. They require an equijoin predicate (a predicate comparing records from one table with those from the other table using a conjunction of equality operators '=' on one or more columns). Classic hash join The classic hash join algorithm for an inner join of two relations proceeds as follows: * First, prepare a hash table using the contents of one relation, ideally whichever one is smaller after applying local predicates. This relation is called the build side of the join. The hash table entrie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LogicBlox
The LogicBlox system is a commercial, declarative, incremental logic programming language and deductive database inspired by Datalog. The LogiQL programming language extends Datalog with several features, including stratified negation, aggregation, and a module system. LogicBlox has been used to build pointer analyses for Java. On December 3, 2014 Predictix acquired LogicBlox. On June 28, 2016 Infor acquires Predictix. Features * Stratified negation * Aggregate functions * Evaluation using a novel worst-case optimal join algorithm. * Data constructors * Static typing * A module system * Probabilistic programming features * Incremental computation * Debugging with provenance References Notes Sources * * * Further reading * {{Cite book , last1 = Halpin , first1 = Terry , url = https://books.google.com/books?id=UBYeBQAAQBAJ&dq=logicblox&pg=PP1 , title = LogiQL: A Query Language for Smart Databases , last2 = Rugaber , first2 = Spe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
E-matching
In computer science, an e-graph is a data structure that stores an equivalence relation over terms of some language. Definition and operations Let \Sigma be a set of uninterpreted functions, where \Sigma_n is the subset of \Sigma consisting of functions of arity n. Let \mathbb be a countable set of opaque identifiers that may be compared for equality, called e-class IDs. The application of f\in\Sigma_n to e-class IDs i_1, i_2, \ldots, i_n\in\mathbb is denoted f(i_1, i_2, \ldots, i_n) and called an e-node. The e-graph then represents equivalence classes of e-nodes, using the following data structures: * A union-find structure U representing equivalence classes of e-class IDs, with the usual operations \mathrm, \mathrm and \mathrm. An e-class ID e is canonical if \mathrm(U, e) = e; an e-node f(i_1,\ldots,i_n) is canonical if each i_j is canonical (j in 1,\ldots,n). * An association of e-class IDs with sets of e-nodes, called e-classes. This consists of ** a hashcons H (i.e. a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
