1. COMP 530 Database Architecture and Implementation
1. Introduction
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2. Department of Computer Science, HKUST Slide 2
Why Learn DBMS?
You want to find a JOB !!!
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3. Big Names in Database Systems
Company
Product
Remarks
Oracle
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
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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4. Who Needs Database Systems
Typical Applications:
Personnel management
Inventory and purchase order
Insurance policies and customer data
… …
Corporate databases
Web data management
Typical Applications:
Web page management
Personalize web pages
… …
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5. Department of Computer Science, HKUST Slide 5
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?
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 Design
HKUST
Academic Registration database:
students: names, address, …
courses: course-no, course-names, …
classroom: number, location, …
db designer 1
Estate Management database:
classroom: number, location, …
office: number, location, …
faculty-residence: building-no, …
student-residence: hall-no, …
db designer 2
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8. 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 DBMS
Applications
Data Files
User
Inventory
Control
User
Customer
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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10. Department of Computer Science, HKUST Slide 10
A Simple Architecture
SQL
C/C++
Programs
DBMS
Shared facilities:
Backup and recovery
Data storage and access modules
Programming tools, etc.
Databases
Applications
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11. Purposes of Database Systems
Database management systems were developed to handle the difficulties caused by different people writing different applications independently.
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Specifically …
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
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Data 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 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 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
data
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16. Three Levels of Abstraction
Payroll
Inventory
Sales
Company database
Files on disks
view 1
view 2
view n
..……...
Logical
view
Physical
view
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view
logical
physical
View definitions
Logical schema
Physical schema
Application
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18. 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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19. An Example of Data Independence
Data on disk
John Law
… …
1129
Program accessing data directly has to know:
first 4 bytes is an ID number
next 10 bytes is an employee name
program
Schema
Data on disk
John Law
… …
1129
Employee:
ID: integer
Name char(10)
DBMS
program
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Instances 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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21. Department of Computer Science, HKUST Slide 21
Data Models
A collection of tools for describing:
data
data relationships
data semantics
data constraints
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22. Entity-Relationship Model
Example of entity-relationship model
social-security
customer-street
balance
account-number
customer-city
customer-name
DEPOSITER
CUSTOMER
ACCOUNT
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Relational Model
Example of tabular data in the relational model:
customer-
name
social-
security
street
city
account-
number
Johnson
Smith
Jones
Alma
North
Main
Palo Alto
Rye
Harrison
A-101
A-215
A-201
A-217
account-number
balance
500
900
700
750
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24. 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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25. 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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26. Transaction 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 (cont.)
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.
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Storage 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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29. 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 database
designer
More system
oriented
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Database 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
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