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COMP 530 Database Architecture and Implementation
COMP 530 Database Architecture and Implementation
1. Introduction
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Why Learn DBMS?Why Learn DBMS?
You want to find a JOB !!!
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Big Names in Database SystemsBig Names in Database Systems
Company Product RemarksOracle Oracle 8i, 9i,
etc.World’s 2nd largest software company; CEO, Larry Ellison, world’s 2nd richest
IBM DB2, Universal Server
World’s 2nd largest after Informix acquisition in 2001
Microsoft SQL Server, Access
Access comes with MS Office
Sybase Adaptive Server
CEO John Chen, grown up in HK
Oracle MySQL Open Source, acquired by Sun in 2007, which was acquired by Oracle in 2009
Postgres “World’s most advanced Open Source DBMS”
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Who Needs Database SystemsWho Needs Database Systems
Corporate databases
Web data management
Typical Applications:Personnel managementInventory and purchase orderInsurance policies and customer data… …
Typical Applications:Web page managementPersonalize web pages… …
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There is a difference between DBMSs (Database Management Systems) and Databases
A few people work for Oracle, etc., to develop, enhance or maintain their DBMS products
Most people make a living working as DB designers, DB programmers or DB Administrators
There is a difference between DBMSs (Database Management Systems) and Databases
A few people work for Oracle, etc., to develop, enhance or maintain their DBMS products
Most people make a living working as DB designers, DB programmers or DB Administrators
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What is in a Database?What is in a Database?
• A database contains information about a particular enterprise or a particular application. E.g., a database for an enterprise may contain everything
needed for the planning and operation of the enterprise: customer information, employee information, product information, sales and expenses, etc.
You don’t have to be a company to use a database: you can store your personal information, expenses, phone numbers in a database (e.g., using Access on a PC).
As a matter of fact, you could store all data pertinent to a particular purpose in a database.
This usually means that a database stores data that are related to each other.
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Database DesignDatabase Design
HKUST
db designer 2
db designer 1
Academic Registration database:
students: names, address, …courses: course-no, course-names, …classroom: number, location, …
Estate Management database:
classroom: number, location, …office: number, location, …faculty-residence: building-no, … student-residence: hall-no, …
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Is a database the same as a bunch of files?
Is a database the same as a bunch of files?
• You can store data in a file or a set of files, but …– How do you input data and to get back the data from
the files?
• A database is managed by a DBMS.
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Before we have DBMSBefore we have DBMS
UserInventoryControl
Applications Data Files
UserCustomer
Order
Question: When a customer ordered 10 PC monitors, how many files do you have to update? Key issues: data sharing,
data redundancy
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A Simple ArchitectureA Simple Architecture
SQL
C/C++ Programs
DBMS
ApplicationsDatabases
Shared facilities:• Backup and recovery• Data storage and access
modules• Programming tools, etc.
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Purposes of Database SystemsPurposes of Database Systems
Database management systems were developed to handle the difficulties caused by different people writing different applications independently.
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• A DBMS attempts to resolve the following problems:– Data redundancy and inconsistency by keeping one copy
of a data item in the database – Difficulty in accessing data by provided query languages
and shared libraries– Data isolation (multiple files and formats)– Integrity problems by enforcing constraints (age > 0)– Atomicity of updates– Concurrent access by multiple users– Security problems
Specifically …Specifically …
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Data IndependenceData Independence
• One big problem in application development is the separation of applications from data
• Do I have change my program when I …– replace my hard drive?– store the data in a b-tree instead of a hash file?– partition the data into two physical files (or merge two
physical files into one)?– store salary as floating point number instead of integer?– develop other applications that use the same set of data?– add more data fields to support other applications?– … …
Independence between Data and Programs/Applications
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Data IndependenceData Independence
• Ability to modify a schema definition in one level without affecting a schema definition in the next higher level.
• The interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others.
• Two levels of data independence:- Physical data independence- Logical data independence
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Data AbstractionData Abstraction
• The answer to the previous questions is to introduce levels of abstraction of indirection.
• Consider how do function calls allow you to change a part of your program without affecting other parts?
Main Program
functions
functions
data
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Three Levels of AbstractionThree Levels of Abstraction
view 1 view 2 ..……... view n
Logical view
Physical view
Payroll Inventory Sales
Company database
Files on disks
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view
logical
physical
View definitions
Logical schema
Physical schema
Application
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Three Levels of Abstraction (cont.)Three Levels of Abstraction (cont.)
• Physical level: describe how a record is stored on disks.•e.g., “Divide the customer records into 3 partitions and
store them on disks 1, 2 and 3.”• Logical level: describes data stored in database, and
the relationships among the data. Similar to defining a record type in Pascal or C:Type customer = record
name: string;street: string;city: integer; end;
• View level: Define a subset of the database for a particular application. Views can also hide information (e.g. salary) for security purposes.
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An Example of Data IndependenceAn Example of Data Independence
John Law … …1129Data on disk
programProgram accessing data directly has to know:• first 4 bytes is an ID number• next 10 bytes is an employee name
John Law … …1129Data on disk Employee:ID: integerName char(10)
Schema
program
DBMS
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Instances and SchemasInstances and Schemas
• Each level is defined by a schema, which defines the data at the corresponding level– A logical schema defines the logical structure of the
database (e.g., set of customers and accounts and the relationship between them)
– A physical schema defines the file formats and locations
• A database instance refers to the actual content of the database at a particular point in time. A database instance must conform to the corresponding schema
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Data ModelsData Models
• A collection of tools for describing:– data– data relationships– data semantics– data constraints
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Entity-Relationship ModelEntity-Relationship Model
• Example of entity-relationship model
CUSTOMER
social-security
customer-name
customer-street
customer-city
DEPOSITER ACCOUNT
account-number balance
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Relational ModelRelational Model
Example of tabular data in the relational model:
customer- name
social- security
customer- street
customer- city
account-number
JohnsonSmithJohnsonJonesSmith
192-83-7465019-28-3746192-83-7465321-12-3123019-28-3746
AlmaNorthAlmaMainNorth
Palo AltoRyePalo AltoHarrisonRye
A-101A-215A-201A-217A-201
account-number balanceA-101A-201A-215A-217
500900700750
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Data Definition Language (DDL)Data Definition Language (DDL)
• Specification notation for defining the database schema– Express what were in the previous two slides to the DBMS
in a formal language
• Data storage and definition language - special type of DDL in which the storage structure and access methods used by the database system are specified
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Data Manipulation Language (DML)Data Manipulation Language (DML)
• Language for accessing and manipulation the data organized by the appropriate data model
• Two classes of 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
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Transaction ManagementTransaction Management
•A transaction is a collection of operations that performs a single logical function in database application
time
Transaction 1
Transaction 2
Conflicting read/write
Transaction 1
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• Transaction-management component ensures that the database remains in a consistent (correct) state despite system failures (e.g. power failures and operating system crashes) and transaction failures.
• Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database.
Transaction Management (cont.)Transaction Management (cont.)
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Storage ManagementStorage Management
• A storage manager is a program module that provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system.
• The storage manager is responsible for the following tasks:– interaction with the file manager– efficient storing, retrieving, and updating of data.
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Database Administrator (DBA)Database Administrator (DBA)
• Coordinates all the activities of the database system; the database administrator has good understanding of the enterprise’s information resources and needs.
• Database administrator’s duties include:– Schema definition– Specifying integrity constraints– Storage structure and access method definition– Schema and physical organization modification– Granting user authority to access the database– Acting as liaison with users– Monitoring performance and responding to changes in
requirements
Primary job of a databasedesigner
More systemoriented
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Database UsersDatabase Users
• Users are differentiated by the way they expected to interact with the system
• Application programmers– Develop applications that interact with DBMS through DML calls
• Sophisticated users– form requests in a database query language– mostly one-time ad hoc queries
• End users– invoke one of the existing application programs (e.g., print
monthly sales report)– Interact with applications through GUI