Week1: Intro Databases

The main components of databases and DBMS.

What is a database?

A database is a big collection of data. There are two types, Relational databases and non SQL or graph databases

What is a row?

A row is a single record in a database table that contains related data across different columns. It is also called a tuple.

What is a column?

The vertical set of data, which are the atype of attributes a record has.

What is a DBMS?

A Database Manage is a software application that interacts with databases to manage data creation, retrieval, updating, and deletion, providing users with a systematic way to store and organize data.

Why do we need DBMS?

• Cocurrent Data Access (multi use)

• Data Organisation and management

• Reduced redundancy

• Data Integrity and accuracy

What are the disadvantages of using DBSMs?

• For small datasets, the overhead of seeting up the DBMS outweighs benefits

• Traditional DBMSs may be too rigid for highly unstructured or rapidly changing data

• Optimised file formats may be more efficient for purely archival or bulk read data.

1-st Tier architecture

The user works directly with the database on the same system. The client, server and database are all in one application. There is no seperate server.

Advantages of 1-st Tier Architecture

• Simple to set up

• Single machine to maintain

• Cost effective

  • Easy to implement

Disadvantages of 1-st Tier architecture

• Limited to a single user

• Poor security

• No centralised control (hard for backups)

  • Hard to share data

2-nd Tier architecture

The application at the clientend directly communicate with the database. There is a client tier and database tier

Advantages of 2-nd tier architecture

• easy to access and fast retrieval

• scalable, can scale by adding clients

  • easier and lower cost than tier 3

Disadvantages of 2-nd tier architecture

• Limited scalability - server can slow

• data leaks as clients are onnected directly to the database

• tight coupling as the client/server are closely linked

  • maintanace growth

3rd tier architecture

The client interacts with an application server and then a query processing and transaction management takes place. We have user - processing - database

Advantages in 3rd tier architecture

• Enhanced salability - individual connections don’t have to be made

• Middle layer keeps data integrety

• Prevention of direct access to server

Disadvantages of 3rd Tier architecture

• Communication points are doubled

• Difficult to interact

• Slower response

  • Higher cost

What is a data model?

A data model is a representation of a data structure that defines relationships between data elements.

What is a database schema?

It is the physical implementation of a data model witha specific DBMS

When may redundancy be created?

1. Repeating data

2. Storing derived attributes

3. Adding checksums

What is controlled redudancy?

It can be used to:

• protect against attacks through checksums

• increase temporal efficiency

• improve performance of queries

We want DBMS transactions to be…

• Atomic - transactions to be treated as a unit

• Consistent - ensure that transactions only make changes to table in predefined ways

• Isolated - the database is left in the same state it was found

• Durable - Its effects will remain committed incase of a crash

What are the different types of constraints?

• Implicit - those enforced by the data model

• Explicit - Those enforced by the schema

• Semantic - Those enforced by the application.