Query processing involves translating queries into a form the database management system can use to efficiently retrieve the desired data. It includes parsing queries, translating them into relational algebra expressions, optimizing the query plan to minimize costs, and executing the optimal plan. The key steps are translation, optimization of multiple evaluation plans based on statistics, and execution of the selected lowest-cost plan to return results. Query processing is crucial for large databases to return results in a timely manner.

1. SEMINAR
MOBILE COMPUTING

2. QUERY PROCESSING
MODULE 2

3. Query processing
Query processing is a scientific art of obtaining the desired
information from a database system in a predictable and reliable
fashions.[2].
Query processing refers to the range of activities involved in
extracting data from a database.
During transactions with a database ,queries are send to read and get
the records.
Query processing means making a correct as well as efficient
execution strategy by query decomposition and query optimization.

4. The activities are:-
Translation of query in high level database languages into expression that can
be used at the physical level of the file system.
A variety of query-optimizing transformations.
Actual evaluation of process.

5. Parsing and translation
• Translate the query into its internal forms . This is then translated
into relational algebra.
• Parser checks syntax , verifies relations.
Evaluation
The query-execution engine takes a query –evaluation plan , executes
that plan , and returns the answers to the query.

6. Query optimization
• Amongst all equivalent evaluation plans choose one with lowest cost.
• Cost is estimated using statistical information from the data base
catalog.

7. INPUT QUERY
RELATIONAL ALGEBRA
ERPRESSION
OPTIMISER
EVALUATION
ENGINEOUTPUT QUERY
STATIC OF DATA
STEPS IN QUERY PROCESSING

8. • Most queries submitted to a DBMS are in high level language such as SQL .
During the parsing and translation stage , human readable form of query is
translated into form usable by the DBMS. These can be in the form of a relational
algebra expressions.
• After parsing and translation into a relational algebra expression the query is then
transformed in to query tree or graph , that can be handled by optimization engine.
• The optimization engine then perform various analysis on the query data ,
generating a number of valid evaluation plans . From there it determines the most
appropriate evaluation plan to execute.
• After the evaluation plan has been selected ,it is passed into the DBMS query
execution engine ,where plan is executed and the result are returned.

9. Conclusion
• One of the most important functional requirements of a database
system is its ability to process queries in timely manner. This is
particularly true for very large, mission critical applications such as
weather forecasting , banking systems and aeronautical applications ,
which can contain millions and even trillions of records . The need for
faster and faster, immediate results never ceases . Thus , a great deal
of research and resources is spent on creating smarter ,highly
efficient query optimization engines.

10. References
[1].Mobile computing ,Raj Kamal–textbook
[2].Introduction to query processing and optimization-
IJARCSSE,2013,vol 3,issue 7
[3].Introduction to Query Processing and Optimization-Michael L . Rupley