Database system concepts and architecture Sept. 2012Yangjun Chen ACS-39021 Outline: Concepts and...

Database system concepts and architecture

Sept. 2012 Yangjun Chen ACS-3902 1

Outline: Concepts and Architecture(Chapter 2 – 3rd, 4th, 5th, and 6th ed.)

• Database schema

• Working process with a database system

• Database system architecture

• Data independence concept

• Database language

• Database application

• Interfaces

• Database environment



Schema: a description of a database -- meta data

• the intension of the database

Schema evolution: if the database definition changes, we say it evolves.

Database State: the data in the database at a particular point in time

• the extension of the schema



Sample database

Student Name StNo Class Major

Smith 17 1 CS

Brown 8 2 CS

Course CName CNo CrHrs Dept

Database 8803 3 CS

C 2606 3 CS

Section SId CNo Semester Yr Instructor

32 8803 Spring 2000 Smith

25 8803 Winter 2000 Smith

43 2606 Spring 2000 Jones

Grades StNo SId Grade

17 25 A

17 43 B



University database schema:

Course

Cnamestring(20)

CNo string(20)

CrHrs integer

Dept.String(20)

gradesStNo integer

SId integer

GradeString(20)

Student

Name string(20)

StNo integer

Class integer

Major String(20)

SectionSID integer

CNo string(20)

Semester integer

Yr integer

Instructor string(20)



Schema evolution:

Course

Cnamestring(20)

CNostring(20)

CrHrs integer

Dept.String(20)

Student

Name string(20)

StNo integer

Class integer

Major String(20)

PrerequisiteCNo string(20)

Pre-CNo string(20)… ...

new table added



Database evolution:

Course

Cnamestring(20)

Cnostring(20)

CrHrs integer

Dept.String(20)

Student

Name string(20)

StNo integer

Class integer

Major String(20)

Age integer

Sex string(20)

… ...

new attributes added



Sample database


Smith 17 1 CS

Brown 8 2 CS


Database 8803 3 CS

C 2606 3 CS




43 2606 Spring 2000 Jones

Grades StNo Sid Grade

17 25 A

17 43 B



Database state changed:


Smith 17 1 CS

Brown 8 2 CS


Database 8803 3 CS

C 2606 3 CS




Grades StNo Sid Grade

17 25 A

17 43 B



Definition

Manipulation

Construction

We define the database

database state is the empty state with no data

initial state when database is populated (loaded)

current state changes with each insert, delete, update

hopefully, the database goes from one correct/valid state to another



Three-schema architecture

Externalview

Externalview

Conceptualschema

Internalschema

Physical storage structures and details

Describes the whole database for all users

A specific user or groups view of the database



Data independence

Ability to change the database at one level with no impact to the next higher level

• physical data independence - the ability to change the physical schema without affecting the conceptual schema

• typical example: add a new index

• logical data independence - the ability to change the conceptual schema without affecting existing external views or application programs

• typical example: add an attribute



DBMS Languages

Data definition language (DDL): used to define the data schema. Ideally one schema definition language per level

• in practice there might be one for all levels

• SQL provides DDL capabilities for the conceptual and external levels



DDL - Examples:

• Create schema: Create schema COMPANY authorization JSMITH;

• Create table: Create table EMPLOYEE

(FNAME VARCHAR(15) NOT NULL, MINIT CHAR, LNAME VARCHAR(15) NOT NULL, SSN CHAR(9) NOT NULL, BDATE DATE, ADDRESS VARCHAR(30), SEX CHAR, SALARY DECIMAL(10, 2), SUPERSSN CHAR(9), DNO INT NOT NULL,

PRIMARY KEY(SSN),FOREIGN KEY(SUPERSSN) REFERENCES EMPLOYEE(SSN),FOREIGN KEY(DNO) REFERENCES DEPARTMENT(DNUMBER));



DBMS Languages

Data Manipulation language (DML): Used to manipulate data.

• typical systems provide a general purpose language for inserting, updating, deleting, and retrieving data

• two distinctions: set-oriented and row-at-a-time



DML - Examples:

• Insert• Update• Delete

INSERT INTO employee ( fname, lname, ssn, dno )VALUES ( "Joe", "Smith", 909, 1);

UPDATE employee SET salary = 100000WHERE ssn = 909;

DELETE FROM employee WHERE ssn = 909;

Query: Select salary from employee;



Set-oriented operations

• select Name, StNo from student where Name like “M%”

• EXEC SQL DELETE FROM authors WHERE au_lname = 'White'

Record-at-a-time

• procedural - need loops, etc

• navigate through data obtaining 1 record at a time

• note that SQL does permit this via cursors



EXEC SQL DECLARE C1 CURSOR FORSELECT au_fname, au_lname FROM authors FOR BROWSE;EXEC SQL OPEN C1;while (SQLCODE == 0){

EXEC SQL FETCH C1 INTO :fname, :lname;print (“the author name is:”, fname, laname);

}

Database applicationsIf an application program that accesses the database embeds DML commands within it, then we have a host language and a data sublanguage.



DBMS interfaces

• menu-based

• forms-based

• GUI – Graphic User Interface

• natural language

• for parametric users

• for dba



Example of a menu-based interface: from MS Access



Example of a GUI from StarTracker



Example of a natural language interface: (from MS SS7)

English Query translates a natural-language question about data in the database to a set of SQL SELECT statements that can then be executed against the SQL Server database to get the answer.

For example, given a car sales database, an application can send English Query a string containing the question, “How many blue Fords were sold in 2011?”

English Query returns to the application an SQL statement such as:

SELECT COUNT(*) FROM CarSales

WHERE Make = 'Ford’ AND Color = 'Blue'

AND DATEPART(yyyy, SalesDate) = ’2011'

The application can then execute the SQL statement against the SQL Server database to get a number. It can return to the user.

Note the comment: English Query works best with a normalized database.



DBMS environment

see figure 2.3• stored data manager

A module to control access to DBMS information that is stored on disk, whether it is part of the database or the catalog.

• DDL compiler

A module to process schema definition, specified in the DDL, and store description of the schema (meta-data) in the DBMS catalog.

• DML compiler

It translates the DML commands into object code for database access.• run-time database processor

It handles database access at run time; it receives retrieval or update operations and carries them out on the database.



A DDL statement: Create table EMPLOYEE

(FNAME VARCHAR(15) NOT NULL, MINIT CHAR, LNAME VARCHAR(15) NOT NULL, SSN CHAR(9) NOT NULL, BDATE DATE, ADDRESS VARCHAR(30), SEX CHAR, SALARY DECIMAL(10, 2), SUPERSSN CHAR(9), DNO INT NOT NULL,

PRIMARY KEY(SSN),FOREIGN KEY(SUPERSSN) REFERENCES EMPLOYEE(SSN),FOREIGN KEY(DNO) REFERENCES DEPARTMENT(DNUMBER));



REL_NAME ATTR_NAME ATTR_TYPE MEMBER_OF_PK MEMBER_OF_FK FK_RELATION

EMPLOYEE FNAME VSTR15 no no

EMPLOYEE SUPERSSN STR9 no yes EMPLOYEE

EMPLOYEE DNO INTEGER no yes DEPARTMENT

... ...

... ...

REL_AND_ATTR_CATALOG

Meta data in System Catalog:



DBMS environment

• query compiler

It handles high-level queries that are entered interactively. It parses, analyzes, and compiles or interprets a query by creating database access code, and then generates calls to the rum-time processor for executing the code.

• pre-compiler

It extracts DML commands from an application program which is written in host programming language like C, Pascal, etc.



DBMS utilities• loading

loading existing files - such as text files or sequential files - into the database.

• Backup

creating a backup copy of the database, usually by dumping the entire database into tape.

• file reorganization

reorganizing a database file into a different file organization to get a better performance.

• performance monitoring

monitoring database usage and providing statistics to the DBA.



Classifying DBMSs

data model:

Relational /object-oriented/hierarchical/network/object-relational

users: single-user/multi-user

location: distributed/centralized

cooperation: homogeneous/heterogeneous

OLTP: on-line transaction processing

• Used to run the day-to-day operations of a business

• event-oriented: take an order, make a reservation, payment for goods, withdraw cash, ...


employee

department

project

dependent

With attributes, etc:

works for

manages

works on

dependents of

controls

supervision

bdate

ssn

name

lnameminitfname

sex address salary

birthdatename sex relationship

name number location

name number location

number ofemployeesstartdate

hours

1

1

1

N

supervisor

supervisee M

N

11

NNdegree

1 N


ER-to-Relational mapping

1. Create a relation for each strong entity type

2. Create a relation for each weak entity type• include primary key of owner (an FK - foreign key)• owner’s PK + partial key becomes PK

3. For each binary 1:1 relationship choose an entity and include the other’s PK in it as an FK. Include any attributes of the relationship

4. For each binary 1:n relationship, choose the n-side entity and include an FK w.r.t the other entity. Include any attributes of the relationship


5. For each binary M:N relationship, create a relation for the relationship• include PKs of both participating entities and any

attributes of the relationship• PK is the concatenation of the participating entity PKs

6. For each multivalued attribute create a new relation• include the PK attributes of the entity type• PK is the PK of the entity type and the multivalued

attribute

7. For each n-ary relationship, create a relation for the relationship• include PKs of all participating entities and any attributes

of the relationship• PK may be the concatenation of the participating entity

PKs

Database system concepts and architecture Sept. 2012Yangjun Chen ACS-39021 Outline: Concepts and...

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