1. Query Caching in Agent-based Distributed Information Retrieval
Query Caching in Agent Based DIR
September 27, 2002
Query Caching in Agent-based Distributed Information Retrieval
Hemali Majithia
October 24, 2002
Hemali Majithia - CADIP, UMBC
Hemali Majithia, CADIP, UMBC

2. Hemali Majithia - CADIP, UMBC
Problem Definition
DIR (IR) systems access their collections to perform searches and answer queries
Query resolution on large corpora is expensive in terms of time and resources
Similar queries produce similar results
Repetitive and redundant searching of the collections
Resource Wastage and Inefficiency
Solution – “ CACHING QUERIES ”
October 24, 2002
Hemali Majithia - CADIP, UMBC

3. Hemali Majithia - CADIP, UMBC
Solution
Caching Mechanism
Cache new queries along with the results
Answer future similar queries using the cached queries
New Query
Query which has not been answered before
Similar Query
Query which is identical or similar to the queries existing in the cache
Emphasis
If similar queries exist, you can retrieve the results for those queries from the previous searched queries rather than exact match
Retrieval  linear time  collection size
October 24, 2002
Hemali Majithia - CADIP, UMBC

4. Hemali Majithia - CADIP, UMBC
Caching Mechanism
Two level Caching Mechanism
First level  Exact Match
Second level  Inverted Index of the queries
Caching Algorithm
Least Recent Used (LRU)
Least Frequent Used (LFU)
Lowest Relative Value (LRV)
Similarity Metric
Cosine Similarity
October 24, 2002
Hemali Majithia - CADIP, UMBC

5. Hemali Majithia - CADIP, UMBC
Caching in CARROT–II
Node I
Node II
Secondary
Cache
Primary
cache
5. Miss
Query
Agent
4. Query forwarded
9.. Update cache
10. Results returned
1. User query
11. Response
6. Query forwarded
to best C2 C2
Agent C2
Agent C2
Agent C2
Agent C2
Agent C2
Agent
3. MISS
2. Lookup
8. HIT
7. Lookup
October 24, 2002
Hemali Majithia - CADIP, UMBC

6. Metrics for Evaluation of Caching Mechanism
Efficiency
Round Trip Time (RTT) = Total time to answer queries fired at the system
Hit Rate = For each agent cache and total hit rate
Cost of caching = The over head caused by caching (assuming that the HIT rate is 0)
Effectiveness
Precision = fraction of retrieved documents that are relevant
Recall =fraction of relevant documents that are retrieved
October 24, 2002
Hemali Majithia - CADIP, UMBC