Introduction

Ellen WalkerCPSC 356 Database Design

Hiram College

CPSC 356: Database Design

• Sources of information– Ellen Walker (walkerel@hiram.edu)

– Web page (http://cs.hiram.edu/~walkerel/cs356)Syllabus handout (available on the web page)

Database Implementation

Projects• External clients • Clients will…

– Meet with you within the next two weeks

– Approve each of 3 major phases– Attend presentations on the last day of class

– Help me to evaluate your projects• You may find your own client, but you cannot be your own client

Database Implementation

Projects• You will…

– Each take a role on the project (see overview document) and switch roles for each phase

– Meet regularly (at least once a week) - in person or electronically (and keep minutes)

– Submit preliminary reports and final phase deliverables as specified in the syllabus. (Only final deliverables are graded).

– Submit confidential evaluations of your group members with each deliverable.

Project Groups

• Usually, projects are done by groups of 3-4 people

• We have 5 in the class– Divide into 2 groups (2, 3)– Work as a single group (5)

Entrepreneurial Mindset

• “A way of thinking and acting to create a new product, service or activity that satisfies a need and adds value to one’s self and community” -- from the grant proposal

• As consultants, you will apply this mindset throughout your project

• At points in the course, we will look at relevant literature and examples of entrepreneurship in the software industry.

What is a Database?

• “Collection of related data”• Usually large (too large to fit in computer memory at once)

• Can be centralized or distributed• Generally accessed by “query” -- retrieving only “relevant” parts at once

Where are Databases?

• E-commerce (e.g. shopping carts)• Airline & hotel reservation systems

• Credit card bureaus• Manufacturers (e.g. parts, tests, defects)

• Libraries• ERP systems (e.g. SCT Banner)

Where else are databases?

• The human genome project• Finance software (e.g. quicken)

• …

Who Interacts with Databases?

• Creating the System– System Analyst– Database Designer – Application Programmer – Project Manager

• Once the System Exists– Database Administrator– System Administrator– End User

Advantages of Databases

• Redundancy Control• Data Consistency and Integrity• Data Sharing and Integration • Security• Improved Maintenance• Concurrency (without data loss)• Backup & Recovery services

Disadvantages…

• Complexity• Size• Cost (Hardware & Software)• Performance • Conversion• Risk of failure

File-based Systems

• Since the 1950’s…• Methods and vocabulary from paper records

• Custom-programmed individual applications– Sales (enter data, retrieve properties, contact clients)

– Contracts (enter data, record leases)

Terminology

• File - collection of records• Record - set of logically connected data (one instance)

• Field - element of a record• Example:

– File = library card catalog– Record = one card– Field = author’s name

Dream Home Example

• Sales– Property record (address, owner, rooms, rent)

– Client record (name, address, phone,property requirements)

• Contracts– Lease record (client, property, rent, payment info)

– Property record (address, rent)– Client record (name, address, phone)

What’s Wrong?

• Each program stores its own data– No cross-program queries (% of clients that actually rented?)

– Multiply entered data (property addresses)• Cost• Inconsistency

• … in its own format– Incompatible data files– Change the format -> change the program!

• … to satisfy a limited set of queries– Program proliferation!

How to Fix?

• Separate data handling from application program

• Make data definitions standardized and external

• Develop reusable query algorithms to be controlled by external information

Better Definition of Database

• Database: A shared collection of logically related data and a description of data, designed to meet the information needs of the organization.

• Database Management System (DBMS): A software system that enables users to define, create, maintain, and control access to the database.

Data / Program Separation

• In addition to data, database holds meta-data (data about data), e.g. field names and data types.

• DBMS now a single program (for all databases) that acts on both meta-data and data

• Provides a form of data abstraction

Organizing Data

• Entity - a distinct object (noun) to represent

• Attribute - property of an entity• Relationship - association between entities (usually a verb)

• Example– Entities: customer, home– Attributes: name (of customer), address (of home)

– Relationship: customer RENTS home

Database Management System

DatabaseDBMS

Query

Update

Update(non-db op)Query

Transaction

Low-levelOperations

e.g. RelationalAlgebra

High LevelLanguage(e.g. SQL)

DBMS Software

• Data Definition Language– Specifies meta-data (data types, structure, constraints)

• Data Manipulation Language (e.g. SQL)– Insert, update, delete and retrieve data

• Access control– Security, Integrity, Concurrency, Recovery

Components of DBMS Environment

• Hardware (servers, clients, storage)

• Software– DBMS environment (e.g. Access, Oracle)– Application programs

• Data• Procedures (in the “real world”)

– Control the design & use of the database

• People

Database Design

• Find an appropriate schema (organization of attributes into tables) based on– Needs of the entire organization– Efficiency of access– Ease of maintenance– Logical relationships among the attributes (normalization)

Bad Ideas for Database Design

• Representing the same information multiple times in different tables

• Putting entirely unrelated attributes in the same table

• Confusing views and schemas

3 Phase Database Design

• Conceptual Design – Independent of all physical considerations– Validate against requirements (cannot be implemented!)

• Logical Design– Lower-level model for a particular kind of database (Relational vs. Hierarchical vs. Object-oriented)

• Physical Design– Data structures, disk layout, etc.