View Selection In Data Warehouses Research Articles

MVPP-Based Materialized View Selection in Data Warehouses Using Simulated Annealing

The process of extracting data from different heterogeneous data sources, transforming them into an integrated, unified and cleaned repository, and storing the result as a single entity leads to the construction of a data warehouse (DW), which facilitates access to data for the users of information systems and decision support systems. Due to their enormous volumes of data, processing of analytical queries of decision support systems need to scan very large amounts of data, which has a negative effect on the systems’ response time. Because of the special importance of online analytical processing (OLAP) in these systems, to enhance the performance and improve the query response time of the system, an appropriate number of views of the DW are selected for materialization and will be utilized for responding to the analytical queries, instead of direct access to the base relations. Memory constraint and views maintenance overhead are two main limitations that make it impossible, in most cases, to materialize all views of the DW. Selecting a proper set of views of DW for materialization, called materialized view selection (MVS) problem, is an important research issue that has been focused in various papers. In this paper, we have proposed a method, called P-SA, to select an appropriate set of views using an improved version of simulated annealing (SA) algorithm that utilizes a proper neighborhood selection strategy. P-SA uses the multiple view processing plan (MVPP) structure for selecting the views. Data and queries of a benchmark DW have been used in experimental results for evaluating the introduced method. The experimental results show better performance of the P-SA compared to other SA-based MVS methods for increasing the number of queries, in terms of the total cost of view maintenance and query processing. Moreover, the total cost of queries in the P-SA is also better than the other important SA-based MVS methods of the literature when the size of the DW is increased.

Evolutionary game theory approach to materialized view selection in data warehouses

The data warehouse contains a number of views that are used to respond to the system queries. On the one hand, the time consuming process of responding to analytical queries of the data warehouse requires to store intermediate views for efficient query answering, and on the other hand, large numbers and high volumes of intermediate views, make the storage of all views impossible. Hence, choosing the optimal set of views for materialization is one of the most important decisions in the data warehouses design, in order to increase efficiency of query answering. Since the search space of the problem is very large, searching among the collections of all possible views of a data warehouse is very expensive and thus, it is necessary to use methods to solve the problem in an acceptable time. Random methods, such as game theory-based optimization approaches, try to increase the speed of selecting materialized views by finding near optimal solutions. In this article, an evolutionary game theory-based method to materialized view selection in the data warehouse is represented which exploits the multiple view processing plan structure to represent the search space of the problem. In this method, a population of players is created, each of which is a solution to the problem. Three strategies are considered for each player and at each repetition of the game, players attempt to choose the best strategy for themselves. At the end of the game, the final solution is calculated according to the strategies selected by the players. Our empirical evaluations revealed that the proposed method has appropriate convergence for large data warehouses and its execution time is very good. It is also shown that the quality of the solutions of the proposed method is more appropriate than other similar random methods.

A game theory based framework for materialized view selection in data warehouses

Data warehouses exploit On-Line Analytical Processing (OLAP) to make rapid answers for analytical queries. Huge amount of aggregated data within a data warehouse on the one hand, and complex analytical queries raised in a data warehouse on the other hand, increase response time to queries extremely. To solve this problem, a number of views are derived and extracted from original base tables and queries have been answered using them. Since materialization of all possible views is not effective because of limitation of storage and maintenance overhead, selecting an optimal set of views for materialization is crucial to maximize data warehouse performance.In this paper, a game theory based framework for the materialized view selection is proposed. In the proposed framework, query processing and view maintenance costs play a game against each other as two players and continue the game until reach the equilibrium. According to the framework, a new static method, called Game Theory based Materialized View selection (GTMV), has been proposed. Verification of proposed approach has been evaluated using several synthetic and real world datasets. Experimental results show that the GTMV method has better performance comparing previous algorithms and substantially outperform former methods.

TSGV: a table-like structure-based greedy method for materialized view selection in data warehouses

Since a data warehouse deals with huge amounts of data and complex analytical queries, online processing and answering to users' queries in data warehouses can be a serious challenge. Materialized views are used to speed up query processing rather than direct access to the database in on-line analytical processing. Since the large number and high volume of views prevents all of the views from being stored, selection of a proper subset of views to materialization is inevitable. Proposing an appropriate method for selecting the optimal subset of views for materialization plays an essential role in increasing the efficiency of responding to data warehouse queries. In this paper, a greedy materialized view selection algorithm is represented, which selects a proper set of views for materialization from a novel table-like structure. The information in this table-like structure is extracted from a multivalue processing plan. This table-like structure-based greedy view selection (TSGV) method is evaluated using the queries of an analytical database, and the query-processing and view maintenance costs of the selected subset are both considered in this evaluation. The experimental results show that TSGV operates better than previously represented methods in terms of time.

Simulation for View Selection in Data Warehouse

On-Line Analytical Processing (OLAP) tools are frequently used in business, science and health to extract useful knowledge from massive databases. An important and hard optimization problem in OLAP data warehouses is the view selection problem, consisting of selecting a set of aggregate views of the data for speeding up future query processing. We apply one n Estimation of Distribution Algorithms (EDAs) to view selection under a size constraint. Our emphasis is to determine the suitability of the combination of EDAs with constraint handling to the view selection problem, compared to a widely used genetic algorithm. The EDAs are competitive with the genetic algorithm on a variety of problem instances, often finding approximate optimal solutions in a reasonable amount of time.

Detecting redundant materialized views in data warehouse evolution

A data warehouse (DW) can be abstractly seen as a set of materialized views defined over a set of remote data sources. A DW is intended to satisfy a set of queries. The views materialized in a DW relate to each other in a complex manner, through common subexpressions, in order to guarantee high query performance and low view maintenance cost. DWs are time varying. As time passes new materialized views are added in order to satisfy new queries, or for performance reasons, while old queries are dropped. The evolution of a DW can result in a redundant set of materialized views. In this paper, we address the problem of detecting redundant materialized views in a given DW view selection, that is, materialized views that can be removed from DW without negatively affecting the query evaluation or the view maintenance process. Using an AND/OR dag representation for multiple queries and views, we first formalize the process of propagating source relation changes to the materialized views by exploiting common subexpressions between views and by using other materialized views that are not affected by these changes. Then, we provide an algorithm for detecting materialized views that are not needed in the process of propagating source relation changes to the DW. We also show how trivially redundant views can be identified in this process. Finally, we use these results to provide a procedure for detecting materialized views that are redundant in a DW. Our approach considers a broad class of views that includes grouping/aggregation views and is not dependent on a specific cost model.