1. DB and DBMS
Adapted from Silberschatz, Korth and Sudarshan

2. Summary What is a Database (DB)? Data Models DB Schemas and Instances
Database Management System (DBMS)
DB Design
Centralized DBMS Architecture
DBMS Users and Administrators
Advanced DBMS Architectures

3. What is a Database (DB)? A very large, integrated collection of data
Models real-world enterprise
Set of Entities (e.g., Student, Course)
Relationships (e.g., Student is Taking Course)
Associations (e.g., Madonna is Taking CS564)

4. (Logical) Data Models
A collection of tools, at a high abstraction level, for describing
Data manipulation
Data definition, data updating, data querying
Data relationships
Data constraints
Examples of data models
Entity-Relationship (ER)
Relational
Object-based (Object-oriented and Object-relational)
Semistructured (XML)
Other older models:
Network model
Hierarchical model

5. ER Model
Models an enterprise as a collection of entities and relationships
Entity: a “thing” or “object” in the enterprise that is distinguishable from other objects
Described by a set of attributes
Relationship: an association among several entities
Represented diagrammatically by an entity-relationship diagram:

6. ER Model (Cont.) The ER model is static
It does not support operations and data querying
Other weakness
Atomic attributes

7. Relational Model Example of tabular data in the relational model
Attributes
Example of tabular data in the relational model

8. A Sample Relational Database

9. Relational Model Weaknesses Atomic columns
Does not explicitly support relationships

10. Relational Data Manipulation Language (DML)
Language for defining, updating and querying the data organized as relational tables
SQL is the most widely used DML language
Data Definition Language (DDL)
Data Updating Language
Data Query Language
Declarative: user specifies what data is required without specifying how to get those data
Select … From … Where … paradigm
Procedural Language
User specifies how (control) to get data

11. SQL DDL Specification notation for defining the database
Example: create table account ( account-number primary key char(13), balance real)
Data constraints
Domain constraints (char, real)
Key integrity (primary key)
Referential integrity (references)
Assertions check (balance > 0.0)
Authorization

12. SQL DDL: Assertion Example
Every loan has at least one borrower who maintains an account with a minimum balance or $
create assertion balance_constraint check (not exists ( select *
from loan where not exists ( select * from borrower, depositor, account where loan.loan_number = borrower.loan_number and borrower.customer_name = depositor.customer_name and depositor.account_number = account.account_number and account.balance >= 1000)))

13. SQL DDL: Authorization
Forms of authorization on parts of the database:
Read - allows reading, but not modification of data.
Insert - allows insertion of new data, but not modification of existing data.
Update - allows modification, but not deletion of data.
Delete - allows deletion of data.
Forms of authorization to modify the database schema (covered in Chapter 8):
Index - allows creation and deletion of indices.
Resources - allows creation of new relations.
Alteration - allows addition or deletion of attributes in a relation.
Drop - allows deletion of relations.

14. SQL Data Updating Language
Insert
insert Into account values (‘ ’, )
Update
update account
set balance =
where account-number = ‘ ’
Delete
delete from account

15. SQL Query Language Examples
Find the name of the customer with customer-id select customer.customer_name from customer where customer.customer_id = ‘ ’
Find the balances of all accounts held by the customer with customer-id select account.balance from depositor, account where depositor.customer_id = ‘ ’ and depositor.account_number = account.account_number
Application programs generally access databases through one of
Language extensions – host languages -- to allow embedded SQL
SQL procedural languages
Application program interface (e.g., ODBC/JDBC) which allow SQL queries to be sent to a database

16. SQL Procedural Languages
MS Transact SQL
Oracle PL/SQL
Standard?

17. Procedural Constructs
For loop
Permits iteration over all results of a query
Example: find total of all balances at the Perryridge branch declare bal real default 0.0; for r as select balance from account where branch_name = ‘Perryridge’ do set bal = bal + r.balance end for

18. Object Model ODMG standard ODL: Object Definition Language
Persistent classes
Class attributes
Non-atomic attributes
Class relationships
Class methods
Class constraints
Class repositories
OQL: Object Query Language
Object querying
Declarative

19. Object-Relational (OR) Model
Object Model
OR Model
Class
Type
Class repository
Object table
Class relationships
Type references
Class attributes
Type attributes
Non-atomic attributes: set, bag, list and array
Non-atomic attributes: array, nested table (Oracle)
OQL
Extended SQL query language
Extended SQL DDL and Updating
Extend the relational data model by including object orientation and constructs to deal with added data types
Allow attributes of tuples to have complex types, including non-atomic values such as nested relations
Preserve relational foundations, in particular the declarative access to data, while extending modeling power
Provide upward compatibility with existing relational languages

20. OR Model: Non-1NF Relation
Example: library information system
Each book has
title,
a set of authors,
Publisher, and
a set of keywords

21. OR Model: Structured Types and Inheritance
Structured types can be declared and used in SQL
create type Name as (firstname varchar(20), lastname varchar(20)) final
create type Address as (street varchar(20), city varchar(20), zipcode varchar(20))
not final
Note: final and not final indicate whether subtypes can be created
Structured types can be used to create tables with composite attributes
create table customer (
name Name,
address Address,
dateOfBirth date)
Dot notation used to reference components: name.firstname

22. OR Model: Structured Types (cont.)
create type CustomerType as (
name Name,
address Address,
dateOfBirth date,
<instance_methods)> )
not final
Can then create a table whose rows are a user-defined type
create table customer of CustomerType

23. OR Model: Methods Can add a method declaration with a structured type
method ageOnDate (onDate date)
returns integer
Method body is given separately
create instance method ageOnDate (onDate date)
for CustomerType
begin
return onDate - self.dateOfBirth;
end
We can now find the age of each customer:
select name.lastname, ageOnDate (current_date)
from customer

24. OR Model: Inheritance
Suppose that we have the following type definition for people
create type Person (name varchar(20), address varchar(20))
[not final]
Using inheritance to define the student and teacher types create type Student under Person (degree varchar(20), department varchar(20)) create type Teacher under Person (salary integer, department varchar(20))
Subtypes can redefine methods by using overriding method in place of method in the method declaration

25. OR Model: Array and Multiset Types
Example of array and multiset declaration:
create type Publisher as (name varchar(20), branch varchar(20)) create type Book as (title varchar(20), author-array varchar(20) array [10], pub-date date, publisher Publisher, keyword-set varchar(20) multiset )
create table books of Book

26. OR Model: Querying Collection-Valued Attributes
To find all books that have the word “database” as a keyword
select title from books where ‘database’ in (unnest(keyword-set ))
We can access individual elements of an array by using indices
E.g.: If we know that a particular book has three authors, we could write
select author-array[1], author-array[2], author-array[3] from books where title = `Database System Concepts’

27. Comparison of O-O and O-R Databases
Relational systems
simple data types, powerful query languages, high protection
Persistent-programming-language-based OODBs
complex data types, integration with programming language, high performance
Object-relational systems
complex data types, powerful query and procedural languages, high protection
Performance?
It depends on the DBMS Administrator
Note: Many real systems blur these boundaries
E.g. persistent programming language built as a wrapper on a relational database offers first two benefits, but may have poor performance

28. XML: Extensible Markup Language
Defined by the WWW Consortium (W3C)
Originally intended as a document markup language not a database language
The ability to specify new tags, and to create nested tag structures made XML a great way to exchange data, not just documents
XML has become the basis for all new generation data interchange formats.
A wide variety of tools is available for parsing, browsing and querying XML documents/data
Example of XML DBMS
Tamino

29. Schemas and Instances
Schema – the structure of the database at a certain abstraction level
Types of schema
Logical schema: database design according to an underlying logical data model
Example of an ER schema: the database consists of information about an entity set customer and another entity set account and the relationship between them
Other types of schema: relational schema, object schema, OR schema
Relational and OR schemas: SQL DDL
Physical schema: database design at the physical level
Example: the set of customers is an indexed-sequential data file
Instance – the actual content of the database at a particular point in time
Physical Data Independence – the ability to modify the physical schema without changing the logical schema
A fundamental requirement for database management systems
Applications depend on the logical schema
In general, the interfaces between the various levels and components should be well defined so that changes in some parts do not seriously influence others

30. Database Management System (DBMS)
DBMS is a software that supports
Database
Set of programs to access the database
An environment that is both convenient and efficient to use
Benefits of using DBMS
No data redundancy
No duplication of information in different files
Make data access easy
No need to write a new program to carry out each new task
It becomes easy to guarantee integrity constraints
Integrity constraints (e.g. account balance > 0) become “buried” in program code rather than being stated explicitly
Soft to add new constraints or change existing ones

31. DBMS (Cont.) Support for the Transaction concept Atomicity of updates
Failures do not leave database in an inconsistent state since that partial updates are not carried out
Example: Transfer of funds from one account to another should either complete or not happen at all
Controlled concurrent access by multiple users
Uncontrolled concurrent accesses can lead to inconsistencies
Example: Two people reading a balance and updating it at the same time
Support for Security
Soft to provide user access control to all data
Access Efficiency
Query optimization

32. DBMS (Cont.) Families of DBMSs Relational DBMSs
MS SQL Server 2000 (?), Oracle 7
Object-relational DBMSs
Oracle 8-10, IBM DB/2

33. Database Design
The process of designing the general structure of the database
Conceptual Design – Deciding on the database schema at a higher abstraction level than relational or object-relational schemas
ER schema, Object schema
Logical Design – Deciding on the logical database schema implemented by DBMSs
R schema, OR schema
Physical Design – Deciding on the physical layout of the R(OR) database
Mappings
Conceptual schema logical schema
Case tools
Manual task
Logical schema physical schema
DBMS  

34. Database Design (Cont.)
OO Database Design
R Database Design
Object schema
ER schema
This mapping is
a big issue
OR schema
R schema
Physical OR schema
Physical R schema

35. Centralized DBMS Architecture

36. Query Processing 1. Parsing and translation 2. Optimization
3. Evaluation

37. Query Processing (Cont.)
Alternative ways of evaluating a given query
Equivalent expressions
Different algorithms for each operation
Cost difference between a good and a bad way of evaluating a query can be enormous
Need to estimate the cost of operations
Depends critically on statistical information about relations which the database must maintain
Need to estimate statistics for intermediate results to compute cost of complex expressions

38. Transaction Management
A transaction is a collection of operations that performs a single logical function in a database application
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
Recovery manager assures atomicity of updates

39. DBMS Users
Users are differentiated by the way they expect to interact with
the system
Application programmers – interact with system through DML calls
Sophisticated users – form requests in a database query language
Specialized users – write specialized database applications that do not fit into the traditional data processing framework
Naïve users – invoke one of the permanent application programs that have been written previously
Examples, people accessing database over the web, bank tellers, clerical staff

40. Database Administrator
Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprise’s information resources and needs
Database administrator's duties include
Schema definition
Storage structure and access method definition
Schema and physical organization modification
Granting user authority to access the database
Specifying integrity constraints
Acting as liaison with users
Monitoring performance and responding to changes in requirements

41. Advanced DBMS Architectures
Client-server
Two-tier
Three-tier
Parallel (multi-processor)
Distributed
Data Grid

42. DBMS Architectures (Cont.)