query processing. 2 basic concepts query processing – activities involved in retrieving and...
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Query Processing
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Basic Concepts Query Processing – activities
involved in retrieving and manipulating data from the database: SQL query translation into low-level
language implementing relational algebra
Query execution
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Phases of Query Processing
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Relational Algebra
Relational algebra defines basic operations on relation instances
Results of operations are also relation instances
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Operations
Most of these operation can be summarized as being concerned with: Manipulation (editing and modifying) Presentation Analysis (indexing and searching)
Range of Operations
Operation
Text Audio Graphic Image Animation Video
Manipulation
• Character• String• Editing
•Sample•Waveform•Audio editing
•Primitive editing•Structural editing•Shading
•Geometric•Pixel operation•Filtering
•Primitive editing•Structural editing
•Frame manipulation•Pixel operation
Presentation
• Formatting• Encryption• Sorting
•Synchronization•compression•Conversion
•Mapping•compression•Lighting•Rendering•viewing
•Compositing•Compression•conversion
•Synchronization•Compression• rendering
•Synchronization•Compression•Video effects•Mixing•conversion
Analysis •Indexing•searching
•Indexing•searching
•Indexing•searching
•Indexing•searching
•Indexing•searching
•Indexing•searching
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Query Decomposition
Analysis Normalization Semantic analysis Simplification Query restructuring
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Relational Algebra Expressions
The result of a relational operation is a relation instance
Relational algebra expression combines relation instances using relational algebra operations
Relational algebra expression produce the result of a query
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Simple SQL Query
SELECT <select-list>FROM <table ist>WHERE <search condition>Group By <grouping column list>Having <search condition>
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Conceptual Evaluation Strategy for Simple Query Compute the cross-product of
tables in from-list Delete those rows which fail the
qualification condition Delete all columns that do not
appear in the select-list If DISTINCT clause is specified,
eliminate duplicate rows.
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Nested Queries Query block:
Single SELECT_FROM_WHERE expression
May include GROUP BY and HAVING Query block – basic unit that is
translated into RA expression and optimized
SQL query is decomposed into query blocks
Querying MMDBMS
Process of querying multimedia can approach in two ways: ‘What’ information can be retrieved ‘How’ information can be retrieved
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‘What’ Approach
Divided into 3 levels of complexity Level 1, Retrieval of Primitive
Features Such as color, shape, texture, spatial location and
object movement. Query Ex.: “Find clips of objects flying from top-right
to bottom-left of screen”
Level 2, Retrieval of Logical Process Related to the identity of object within the media Query Ex.: “Find a clips of an aero plane taking-off”
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‘What’ Approach (cont.) Level 3, Retrieval of Abstract
Attributes Associated with an understanding of the nature or
purpose of the object Query Ex.: “Find a picture of nutritional disasters”
Level 2 and 3 are regarded as Semantic Media Retrieval.
However, Success in answering multimedia query is largely limited to level 1. The difference between simple queries at level 1 and those at level 2 and 3 has been called the semantic gap.
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‘How’ Approach
This approach can be classified on the basis of whether is retrieved by: Attribute-based retrieval Text-based retrieval Content-based retrieval
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‘How’ Approach
Attribute-based retrieval (ABR) ABR is a method that uses a set of structured attributes in
the same way as traditional DBMS. It uses essentially the similar principles, except that these
must be able to cope with gigantic media object such as video clip.
This method can be particularly effective with text. However, the method does not make use of the rich content of image and retrieve information so that is essentially limited to level 1 queries.
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‘How’ Approach
Text-based retrieval (TBR) TBR methods work by adding annotations, usually brief
descriptions combined with some structured data. An example of system with this capability was the Kodak’s
picture exchange. Disadvantage of the system is that they are very difficult in
practice.
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‘How’ Approach
Content-based retrieval (CBR) CBR is developed to try to overcome some of the
difficulties of TBR. The idea is that the important details can be extracted
from the media by automatic method which will be more efficient for data
capture and reliable for retrieval.
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Ontology Providing a shared understanding of the
application domain that can be communicated between people and computer and incorporated in the database as part of the metadata.
It means that key information about the kind of object in the database can be captured and reused many times for many different queries with any kind of media data.
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Metadata Usage in Querying Considering role of metadata for media
separation Considering design to classify metadata
and relate this to three type of information retrieval Content Independent – used in ABR Content Descriptive – used in TBR Content Dependent – use in CBR
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Role of Metadata in Querying
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Query Metadata
Image Metadata
Media independent
metadata
Meta-Correlation
Text Metadata
Media dependent
Media preprocessor
Media dependent
Media preprocessor
Image Text
Conceptual data view
Ontologies
Physical Storage view
Example of role of metadata in Querying
Query Language
Structured Query Language Query languages are generalized
computer language that is used to interrogate database and information systems.
Query languages can be classified
according to database query languages or information retrieval query languages.
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Structured Query Language (SQL) scope includes data insert, query, update and delete, schema creation and modification, and data access control.
SQL was developed at IBM by Donald D. Chamberlin and Raymond F. Boyce in the early 1970s. This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasi-relational database management system.
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The most common operation in SQL is the query, which is performed with the declarative SELECT statement. SELECT retrieves data from one or more tables, or expressions.
Standard SELECT statements have no persistent effects on the database. Some non-standard implementations of SELECT can have persistent effects, such as the SELECT INTO syntax that exists in some databases.
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Queries allow the user to describe desired data, leaving the database management system (DBMS) responsible for planning, optimizing, and performing the physical operations necessary to produce that result as it chooses.
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A query includes a list of columns to be included in the final result immediately following the SELECT keyword. An asterisk ("*") can also be used to specify that the query should return all columns of the queried tables. SELECT is the most complex statement in SQL, with optional keywords and clauses that include:
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The FROM clause which indicates the table(s) from which data is to be retrieved. The FROM clause can include optional JOIN subclauses to specify the rules for joining tables.
The WHERE clause includes a comparison predicate, which restricts the rows returned by the query. The WHERE clause eliminates all rows from the result set for which the comparison predicate does not evaluate to True.
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The GROUP BY clause is used to project rows having common values into a smaller set of rows. GROUP BY is often used in conjunction with SQL aggregation functions or to eliminate duplicate rows from a result set. The WHERE clause is applied before the GROUP BY clause.
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The HAVING clause includes a predicate used to filter rows resulting from the GROUP BY clause. Because it acts on the results of the GROUP BY clause, aggregation functions can be used in the HAVING clause predicate.
The ORDER BY clause identifies which columns are used to sort the resulting data, and in which direction they should be sorted (options are ascending or descending). Without an ORDER BY clause, the order of rows returned by an SQL query is undefined.
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Query Language
Object Oriented Query Language
Evolution of Design Approach in Multimedia
Object Oriented Query Language
Figure 1 : Media class and Its subclass
Object Oriented Schema Declaration
Event & Content-Based Queries for Image / Video Data
Spatial
Temporal
Spatial Object
Temporal Object
Queries for Multimedia
Multimedia Document Retrieval
Playout Control
Thanks for Your Attention