Short note on Query Processing .

-

Query Processing 

  • Query Processing is a translation of high-level queries into low-level expressions. It is a step-wise process that can be used at the physical level of the file system, query optimization, and actual execution of the query to get the result.
  • It requires the basic concepts of relational algebra and file structure. It refers to the range of activities that are involved in extracting data from the database. It includes the translation of queries in high-level database languages into expressions that can be implemented at the physical level of the file system.
  • Query Processing is the process of converting high-level queries to low-level expressions to extract the data from physical level file systems like databases.  OR,
  • Query Processing would mean the entire process or activity which involves query translation into low-level instructions, query optimization to save resources, cost estimation or evaluation of query, and extraction of data from the database

It involves mainly four steps

  • Parsing and translation
  • Optimization
  • Evaluation
  • Execution





Comments

Post a Comment

Popular posts from this blog

Suppose that a data warehouse for Big-University consists of the following four dimensions: student, course, semester, and instructor, and two measures count and avg_grade. When at the lowest conceptual level (e.g., for a given student, course, semester, and instructor combination), the avg_grade measure stores the actual course grade of the student. At higher conceptual levels, avg_grade stores the average grade for the given combination. a) Draw a snowflake schema diagram for the data warehouse. b) Starting with the base cuboid [student, course, semester, instructor], what specific OLAP operations (e.g., roll-up from semester to year) should one perform in order to list the average grade of CS courses for each BigUniversity student. c) If each dimension has five levels (including all), such as “student < major < status < university < all”, how many cuboids will this cube contain (including the base and apex cuboids)?

-
Image
a) A Snowflake Shema is shown in figure below: b) The specific OLAP operations to be performed: 1. Roll-up on course from course_id to department. 2. Roll-up on a student from student_id to university. 3. Dice on course, student with department ="CS" and university = "biguniversity" 4. Drill-down on a student from the university to student_name. c) N = 4 dimensions The cube will contain 54 = 625 cuboids.
Read more

Suppose that a data warehouse consists of the three dimensions time, doctor, and patient, and the two measures count and charge, where a charge is the fee that a doctor charges a patient for a visit. a) Draw a schema diagram for the above data warehouse using one of the schemas. [star, snowflake, fact constellation] b) Starting with the base cuboid [day, doctor, patient], what specific OLAP operations should be performed in order to list the total fee collected by each doctor in 2004? c) To obtain the same list, write an SQL query assuming the data are stored in a relational database with the schema fee (day, month, year, doctor, hospital, patient, count, charge)

-
Image
Solution: a) Star Schema is shown in the figure below: b) First, we should use the roll-up operation to get the year 2004(rolling-up from the day then month to a year). After getting that, we need to use the slice operation to select (2004). Second, we should use roll-up operation again to get all patients. Then, we need to use the slice operation to select (all). Finally, we get a list of the total fee collected by each doctor in 2004. So, 1. roll up from day to month to year 2. slice for year = “2004” 3. roll up on patient from the individual patient to all 4. slice for patient = “all” 5. get the list of the total fees collected by each doctor in 2004 c) Select doctor, Sum(charge) From fee Where year = 2004 Group by doctor
Read more

Discuss classification or taxonomy of virtualization at different levels.

-
Image
Taxonomy of virtualization Virtualization is mainly used to emulate the execution environment, storage, and networks. The execution environment is classified into two: – Process-level – implemented on top of an existing operating system.  – System-level – implemented directly on hardware and does not or minimum requirement of the existing operating system. OR,  Virtualization covers a wide range of emulation techniques that are applied to different areas of computing. A classification of these techniques helps us better understand their characteristics and use  V irtualization is mainly used to emulate  ● Execution Environments: To provide support for the execution of the programs eg. OS, and Application.  ○ Process Level: Implemented on top of an existing OS that has full control of the hardware  ○ System Level: Implemented directly on Hardware and do not require support from existing OS.  ● Storage: Storage vi...
Read more