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U-DBMS: A Database System for Managing
Constantly-Evolving Data (VLDB 2005)
Reynold Cheng
[email protected]
Hong Kong
Polytechnic University
Sarvjeet Singh, Sunil Prabhakar
{singh35,sunil}@cs.purdue.edu
Purdue University
Sensor Databases
sensor
Database
System
sensor
External Environment
e.g., temperature,
Uncertainty
(e.g.,sampling
Network
moving objects,
error) can
render incorrect
Channel
hazardous materials
query results.
queries
results
sensor
user
R. Cheng, S. Singh, S. Prabhakar
U-DBMS
sensor
Uncertainty Management
uncertainty pdf
Uncertainty
of a Sensor
Data Value
[L


uncertainty interval
R]
Probabilistic Queries: answers with probability
Example: Which item, A and B, is smaller?
 {(A, 0.8), (B, 0.2)}
 A correct (possibly less precise) answer, instead
of a potentially incorrect answer
R. Cheng, S. Singh, S. Prabhakar
U-DBMS
U-DBMS Prototype





Uncertainty-Data Base Management System
Meta-queries for specifying uncertainty interval
and type of uncertainty pdf
Extension of SQL for probabilistic queries
Measurement of query quality
Implemented on PostgreSQL 8.0
R. Cheng, S. Singh, S. Prabhakar
U-DBMS
Architecture of U-DBMS
Uncertainty class
PostgreSQL 8.0
Uncertain data
structures
Probabilistic
Query
Operators
Access Methods
Other data types
Query Evaluation
Engine
Other operators
R. Cheng, S. Singh, S. Prabhakar
U-DBMS
Example Queries
Create a table with UNCERTAIN type
CREATE table T(
k INTEGER primary key,
a UNCERTAIN);
Insert Gaussian pdf (μ,σ)
Insert into T values
(1,‘(g,μ,σ)’);
Display uncertain info. of a if a > 5
SELECT a FROM T where a > 5;
Equality join of uncertain attributes (=% returns
probability of equality)
SELECT R.k, S.k, R.a =% S.a
FROM R,S
WHERE R.a = S.a;
Entities with prob. giving min value of a
(e.g., {(3,0.5), (5,0.3), (11,0.2)})
SELECT Emin(T.a) from T;
Min value of a for table T (UNCERTAIN)
SELECT Vmin(T.a) from T;
R. Cheng, S. Singh, S. Prabhakar
U-DBMS