MANAGING UNCERTAIN DATA USING MONTE CARLO TECHNIQUES

• US 20100312775A1
• Filed: 06/03/2009
• Published: 12/09/2010
• Est. Priority Date: 06/03/2009
• Status: Active Grant

• Current Assignee: International Business Machines Corporation, University of Florida Research Foundation, Incorporated (State University System of Florida)
• Original Assignee: International Business Machines Corporation
• Inventors: Xu, Fei, Jampani, Ravindranath, Wu, Mingxi, Jermaine, Chistopher Matthew, Perez, Luis Leopoldo, Haas, Peter Jay
• Granted Patent: US 8,234,295 B2
• Time in Patent Office: Days
• US Class Current: 707/759
• CPC Class Codes: G06F 16/2462 Approximate or statistical queries

Abstract

According to one embodiment of the present invention, a method for managing uncertain data is provided. The method includes specifying data uncertainty using at least one variable generation (VG) function, wherein the VG function generates pseudorandom samples of uncertain data values. A random database based on the VG function is specified. and multiple Monte Carlo instantiations of the random database are generated. Using a Monte Carlo method, a query is repeatedly executed over the multiple Monte Carlo instantiations to output a Monte Carlo method result and associated query-results. The Monte Carlo method result may then be used to estimate statistical properties of a probability distribution of the query-result.

Claims

1. A method comprising:

specifying data uncertainty using at least one variable generation (VG) function, wherein said VG function generates pseudorandom samples of uncertain data values;

specifying a random database based on said VG function;

generating a number N Monte Carlo instantiations of said random database, wherein N is a number greater than 1;

identifying a database tuple bundle t, wherein the database tuple bundle t is a data structure representing N instantiations of a tuple in the N Monte Carlo instantiations;

executing a query Q over the N Monte Carlo instantiations, wherein said executing comprises;

executing a query plan for the query Q once over the set of all database tuple bundles; and

outputting zero or more numerical values that are used to estimate statistical properties of the probability distribution of the result of the query Q.

2. The method according to claim 1, further comprising representing the database tuple bundle t in a compressed form in which only pseudorandom numbers used to generate the uncertain data values are represented.

3. The method according to claim 2, further comprising expanding the database tuple bundle t represented in the compressed form to an expanded form, wherein the database tuple bundle t is represented in the expanded form when all instantiated attribute values are explicitly represented.

4. The method according to claim 2, where executing the query plan further comprises filtering out tuples based on the compressed form of the database tuple bundle.

5. The method according to claim 1 wherein said outputting comprises outputting a set of pairs (v,f), where each v is a distinct tuple and f is the fraction of said Monte Carlo instantiations in which said tuple v appears at least once in a query result.

6. The method according to claim 5, wherein said query is an aggregation query and further comprising:

computing a table having entries of the form (v,n), wherein v is a query-result and n is the number of N Monte Carlo instantiations in which the query result is equal to v; and

executing a second query over the table to obtain an estimate of a statistical property of the probability distribution of the result of the query Q.

7. The method according to claim 6, wherein the second query computes an average of query-results in the table.

8. The method according to claim 1, further comprising:

maintaining a running statistical property of query-results as each query-result is determined, wherein each query-result corresponds to one of the N Monte Carlo instantiations; and

after N query-results are determined, outputting the final value of the running statistical property to be the estimated statistical property of the probability distribution of the result of the query Q.

9. The method of claim 1, further comprising:

outputting N query-results, wherein each query-result corresponds to one of the N Monte Carlo instantiations; and

using the N query-results, computing an estimate of a statistical property of the probability distribution of the result of the query Q.

10. The method according to claim 9, wherein computing an estimate of a statistical property of the probability distribution of the result of the query Q comprises computing an average of the N query-results and equating the average to be an estimate of the expected value of the probability distribution of the result of query Q.

11. The method according to claim 1, wherein specifying said random database based on the VG function comprises specifying random tables based on the VG function.

12. A method comprising:

specifying data uncertainty using at least one variable generation (VG) function, wherein said VG function generates pseudorandom samples of uncertain data values;

specifying a random database based on said VG function;

generating multiple Monte Carlo instantiations of said random database;

using a Monte Carlo method, repeatedly executing a query over said multiple Monte Carlo instantiations to output a Monte Carlo method result and associated query-results; and

using said Monte Carlo method result, estimating statistical properties of a probability distribution of said query-result.

13. The method according to claim 12, wherein repeatedly executing said query over said multiple Monte Carlo instantiations comprises executing said query over each of said Monte Carlo instantiations to output an associated query-result for each of said Monte Carlo instantiations.

14. The method according to claim 12, wherein specifying said random database based on said VG function comprises specifying random tables based on said VG function.

15. The method according to claim 14, wherein specifying random tables based on said VG function comprises specifying random tables of a relational database based on said VG function.

16. The method according to claim 12, wherein said VG function is user-defined.

17. The method according to claim 16, wherein the VG function is parameterized and is based on results of SQL queries executed over parameter tables stored in a relational database.

18. The method according to claim 17 wherein said specifying random tables comprises using an extension of the SQL Create Table syntax that links uncertain attributes to their corresponding VG functions and specifies how the VG functions are to be parameterized prior to invocation.

19. A system comprising:

a database containing uncertain data values and zero or more parameter tables;

a variable generation (VG) function component that receives the results of SQL queries over said parameter tables as input and that outputs pseudorandom samples of said uncertain data values;

a random database comprising said pseudorandom samples;

a Monte Carlo processor generating multiple Monte Carlo instantiations of said random database;

a query execution component receiving a query and executing a query over said multiple Monte Carlo instantiations to output a Monte Carlo result and associated query-results; and

a statistical property estimator receiving said Monte Carlo result and estimating statistical properties of a probability distribution of said query result.

20. A computer program product for managing uncertain data, said computer program product comprising:

a computer usable medium having computer usable program code embodied therewith, said computer usable program code comprising;

computer usable program code configured to;

specify data uncertainty using at least one variable generation (VG) function, wherein said VG function generates pseudorandom samples of uncertain data values;

specify a random database based on said VG function;

generate multiple Monte Carlo instantiations of said random database;

using a Monte Carlo method, repeatedly execute a query over said multiple Monte Carlo instantiations to output a Monte Carlo method result and associated query-results; and

using said Monte Carlo method result, estimate statistical properties of a probability distribution of said query-result.