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csce520-lect2.a - CSCE 520 Relational Data Model Lecture 2...

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CSCE 520- Relational Data Model Lecture 2
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Note! Homework 1 is available at http://www.cse.sc.edu/~farkas/csce520-2011/h HW 1 is due on Jan. 26, 2011 via dropbox What are the ACID properties of transactions? From the “A First Course in Database System” exercise 2.3.2 all of the questions (page 37) Farkas CSCE 520  2
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Database Management Systems Smaller and smaller systems Past: large and expensive DBMS Present: DBMS in most personal computers More and more data stored Past: few MB Present: terabyte (10 12 bytes), petabyte (10 15 bytes) Farkas CSCE 520  3
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Application Architectures Farkas CSCE 520  4 Two-tier architecture Three-tier architecture
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Database Users Users are differentiated by the way they interact with the system Database Administration (DBA) : responsible for the structure or schema of the database (DDL), coordinates all activities regarding the database Application programmers – interact with system through DML calls Sophisticated users – form requests in a database query language Naive users – invoke one of the permanent application programs that have been written previously Farkas CSCE 520  5
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Data Definition Language (DDL) Defines the database schema and constraints Should be used by DBAs only! DDL compiler data dictionary Metadata – data about data Farkas CSCE 520  6
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Data Manipulation Language (DML) Accessing and manipulating the data DML – query language Query Languages Procedural – user specifies what data is required and how to get those data Nonprocedural – user specifies what data is required without specifying how to get those data SQL: nonprocedural query language Farkas CSCE 520  7
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Transaction Management Transaction : unit of work to be executed atomically and in isolation from other transactions Transaction-manager : ensures that the database remains in a consistent state even in the presence of failures and concurrent users Logging and recovery manager : durability of transactions Concurrency-control : interaction among the concurrent transactions to ensure consistency Deadlock resolution : intervene and cancel blocked transactions Farkas CSCE 520  8
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ACID Properties Atomicity: all-or-nothing of the transaction’s effect will take place Consistency : each transaction leaves the system in a consistent state Isolation : each transaction must appear to be executed as if no other transactions are executed at the same time Durability : effect of a transaction must never be lost after the transaction is completed Farkas CSCE 520  9
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csce520-lect2.a - CSCE 520 Relational Data Model Lecture 2...

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