Database Systems{week 01}

Rensselaer Polytechnic InstituteCSCI-4380 – Database SystemsDavid Goldschmidt, Ph.D.

What is a database?

What is a Database? A collection of organized information

that persists over a long period of time Such information (or data) is managed

by a DataBase Management System

DBMS: Software used to create and manage large

amounts of data efficiently and securely

DBMS characteristics

A typical DBMS is expected to: Provide a means by which users can create

databases and specify their schemas Give users the ability to query the database

(and efficiently return results) Store huge amounts of data Support durability and reliability, recovering

from failures and errors Control user access to data (i.e. security)

Data modeling

Database schemas abstract elements of the real world; to do so, we use a data model

A data model describes: Structure of the data Operations on the data (reads and

writes) Constraints on the data

Take the ACID test (if you dare) Transactional (and other) databases

must meet the ACID test: Atomicity: all-or-nothing execution Consistency: relationships between data

elements must adhere to defined constraints

Isolation: each transaction appears as if it occurs without other database activity

Durability: the data itself is durable in the sense that the data must never be lost

Relational data modeling A relation is a two-dimensional data

structure that consists of a set of attributes and (zero or more) tuples or rows of data

Each attribute takes only simple values i.e. strings, numbers, boolean values, dates, etc.

attribute1 attribute2 attribute3 attribute4Mark Goldberg AE 108 6Mukkai Krishnamoort

hyLally 305 30

Sibel Adali Lally 313 6

firstname lastname office nuttiness

Relational data modeling The relation schema consists of:

The name of the relation The set of attributes The name (and type) of each attribute Other constraints

An example:Profs( firstname, lastname, office, nuttiness )

Relational data modeling A relation contains a set of tuples

Each tuple contains values for all the attributes in the relation schema that are drawn from the domain of that attribute

Example tuples:

possibly empty

( 'Mark', 'Goldberg', 'AE 108', 6 )( 'Mukkai', 'Krishnamoorthy', 'Lally 305', 30 )( 'Sibel', 'Adali', 'Lally 313', 6 )

As a set, tuple order is not significant.

Keys

A key for a relation is a set of attributessuch that no pair of tuples has the same value for the key

Examples: Social Security Number RIN (Rensselaer ID Number) First and last name (would this one

work???)

Given the key, we can query the relation

and expect exactly one result (or zero!).

Profs( firstname, lastname, office, nuttiness )

Primary keys

In practice, keys are used to improve efficiency of queries using such keys And note that not all keys provide

“uniqueness”

Since relations may have multiple keys,a primary key is selected The primary key might be a separate

(unused?) numeric fieldWhat would be the use of this?

Using SQL to store relations To store a relation, we can use SQL

to create a table in a relational database system

Example attribute (data) types include: CHAR, VARCHAR, TEXT BIT, INT, INTEGER, FLOAT, DOUBLE, REAL DECIMAL, NUMERIC DATE, DATETIME, TIMESTAMP BLOB, MEDIUMBLOB, LONGBLOB

Table creation

create table tablename ( attribute1_name attribute1_type, attribute2_name attribute2_type, ... attributeN_name attributeN_type, constraints);

might also have table options here

other attribute constraintsmight be included here

Example table creation

create table student( id int, name varchar(255), major char(4), gender char(1), dob date, constraint student_pk primary key (id));

student_pk is an arbitrary name

why did we specifythese attribute types?

Modifying table structure Removing a table from the schema:

Adding a new attribute to a table:

Removing an attribute from a table:

drop table tablename;truncate table tablename;

what’s the difference?

alter table tablename add attributename attributetype;

alter table tablename drop attributename;

Relational algebra and sets Relational algebra consists of a set

of simple operators that can be used to query the database

Each operator takes as input two relations and produces as output a relation Think of a relation as a set of tuples The input and output relations all must

have the same schema

Set operators

Given two relations R and S that havethe same schema, set operators include: Union:▪ R S { tuples that are in R or S (or both) }

Intersection:▪ R S { tuples that are in both R and S }

Set difference:▪ R – S { tuples that are in R but not in S }remember that a set

does not contain duplicates

Projection (attribute filtering) The projection of a relation R on

attributes A1, A2, ..., An is given by: A1,...,An (R) = { t | t is a tuple in R

and t only contains values for attributes A1, A2, ..., An iff the schema of R contains attributes A1, A2, ..., An }

We use projection to remove existing attributes from R (by selecting a subset of them)

duplicate tuples are omitted!

Selection

Find and select all tuples from relation Rthat satisfy some set of conditions Forms the basis of querying a database The selection C (R) is based on Boolean

condition C over attributes of relation R Example conditions include:▪ A = e, A > e, A >= e, A < e, A <= e, A <> e▪ A1 = A2, A1 <> A2 ▪ Any combination of conditions using AND, OR,

NOT

A, A1, and A2 are attributese is a constant or expression

Selection

Selection selects a subset of tuples in relation R (with the schema unchanged) C (R) = { t | t is a tuple in R and t

satisfies the condition C on relation R }

Selection conditions can only refer toattributes in the given relation R

For conditions spanning multiple relations, we first must combine those relations (i.e. join)

Homework – Part One

Download and install both the Oracle and MySQL database packages noted on the course Web site

Homework – Part Two

Design a full schemato store informationabout celebrities,including: Basic information Relationships (e.g. marriages, flings,

etc.) Issues (e.g. drugs, affairs, addictions,

etc.)