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Introduction to Databases. Week 1, Day 1 (based on Ch 1 of Connolly and Begg). Introduction to Databases - Outline. Before Databases Some history not in the text File Based Approach Illustrated with real world problems Database Approach With simplified advantages & disadvantages.

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introduction to databases

Introduction to Databases

Week 1, Day 1

(based on Ch 1 of Connolly and Begg)

CMPT 355 Sept-Dec 2010 - w1d1

introduction to databases outline
Introduction to Databases - Outline
  • Before Databases
      • Some history not in the text
  • File Based Approach
      • Illustrated with real world problems
  • Database Approach
      • With simplified advantages & disadvantages

CMPT 355 Sept-Dec 2010 - w1d1

before databases outline
Before Databases - Outline
  • Some Basic Concepts
    • Record
    • File
    • Field
  • Accessing Data
    • Sequential Access
    • Direct Access
    • Record Keys
    • Indexed Sequential Access
    • Random Access
  • Some Problem Scenarios

CMPT 355 Sept-Dec 2010 - w1d1

b db some basic concepts
B db – Some Basic Concepts

Record:

  • The name “record” is based on traditional “recorded” documents.
    • Earliest “records” were 80 column punch cards
    • “The card is often called a unit record, because data is restricted to the 80 columns, and the card is read or punched as a unit of information.”1
  • Other definitions
    • “A stored record is an identifiable collection of data elements.”2
    • “A record is some collection of attributes that describe some entity or event.”3

1 Introduction to IBM Data Processing Systems, 1964, IBM, F22-6517-2

2 Introduction to Data Management, 1970, IBM, SC20-8096-0

3 J. Carter, Developing e-Commerce Systems, Prentice-Hall, 2002

CMPT 355 Sept-Dec 2010 - w1d1

b db some basic concepts5
B db – Some Basic Concepts

Record (cont):

  • A record is the basic unit of stored data that an user recognizes.
  • E.g. customer record, sales slip record.
  • Problems
    • Different users may
      • have different records for the same data
      • use different versions of the same record
  • Currently dealt with as records / rows / views.

CMPT 355 Sept-Dec 2010 - w1d1

b db some basic concepts6
B db – Some Basic Concepts

File:

  • Name “file” based on traditional file folders and filing cabinets
    • “A named collection of occurrences of logical records which may be of more than one logical record type; a set of application record values, pertaining to one or more record formats.”1
  • Other definitions
    • “Stored records are grouped on storage volumes as data sets.”2
    • “A collection of similar records that may be used individually or together”3

1 Data Base Concepts, 1971, IBM, ZR20-4219-0

2 Introduction to Data Management, 1970, IBM, SC20-8096-0

3 J. Carter, Developing e-Commerce Systems, 2002, Prentice-Hall

CMPT 355 Sept-Dec 2010 - w1d1

b db some basic concepts7
B db – Some Basic Concepts

File (cont):

  • The basic unit of stored data that an operating system recognizes
  • E.g. Customer file, sales slip file
  • Currently dealt with as a tables.

CMPT 355 Sept-Dec 2010 - w1d1

b db some basic concepts8
B db – Some Basic Concepts

Field:

  • The name “field” is based on traditional “fields” that need to be filled in on forms
    • “A field is the smallest meaningful unit of information of interest.”1
  • Other related definitions
    • “The smallest unit of logical data of concern to a programmer.”2

1 Introduction to Data Management, 1970, IBM, SC20-8096-0

2 Data Base Concepts, 1971, IBM, ZR20-4219-0

CMPT 355 Sept-Dec 2010 - w1d1

b db some basic concepts9
B db – Some Basic Concepts

Field:

  • The basic unit of stored data that a program recognizes
  • E.g. customer name, sales slip id number
  • Problems
    • Does name {first + last} require 1 or 2 fields?
    • How many fields do you use for an address?
    • How many fields are needed on a sales slip to record all items purchased?
  • Currently dealt with as a data attribute.

CMPT 355 Sept-Dec 2010 - w1d1

b db accessing data
B db – Accessing Data

Sequential Access

  • The method of using tape storage. (Consider accessing a song on a cassette tape.)
  • Easiest to use if sorted based on some field of information (usually a record key)
      • “Each file is made up of records, each containing information required to describe completely a single item. The sequence may be by item number, name, account number, or man number, but all files in a single application must be in the same sequence.”1
  • Updates + Old File = New File

1 Introduction to IBM Data Processing Systems, 1964, IBM, F22-6517-2

CMPT 355 Sept-Dec 2010 - w1d1

b db accessing data11
B db – Accessing Data

Record keys

  • According to IBM 1
    • “The data element chosen to order the (sequential) data set is called the key.
    • “The sequence of data may be changed by selecting a different data element to be the key and sorting the stored records according to the values of the new key.
    • “In some cases, using one data element as a key is not sufficient to identify a given stored record. In this case, one or more additional data elements would be concatenated to form the key.”

1 Introduction to Data Management, 1970, IBM, SC20-8096-0

CMPT 355 Sept-Dec 2010 - w1d1

b db accessing data12
B db – Accessing Data

Direct Access

  • The first access method designed to make use of the ability to quickly go to any location on a disk.
  • Records stored in fixed locations based on the values of key fields that can be directly mapped to a physical location on disk.
    • There must be space for records with each possible record key value.
    • Usually record key values are allocated sequentially to ensure that all storage locations are used (at least initially).
  • Records are updated in their original location.

CMPT 355 Sept-Dec 2010 - w1d1

b db accessing data13
B db – Accessing Data

Indexed Sequential Access

  • Optimized access speed with storage space utilization as a major improvement over direct access.
  • Records stored in FCFS manner are quickly accessed by using an index of pointers from record keys to the locations of the records.
    • Index needs to be resorted each time it is updated.
  • Records are updated in their original location.

CMPT 355 Sept-Dec 2010 - w1d1

b db accessing data14
B db – Accessing Data

Random Access

  • Optimized access speed with storage space utilization as a major improvement over direct access.
  • Records stored in at particular locations based on hashing values of the record key.
    • If multiple records hash to the same location, need to be able to deal with as small chains of records.
  • Records are updated in their original location.

CMPT 355 Sept-Dec 2010 - w1d1

b db some problem scenarios
B db – Some Problem Scenarios
  • Me as a Grad Student moving from place to place
    • data redundancy
  • Me trying to get the Registrars people to work with the residence halls
    • data availability
  • Me looking for a book in the library
    • data sharability
  • Me answering a survey about my favorite beer

 data evolvability

CMPT 355 Sept-Dec 2010 - w1d1

file based approach outline
File Based Approach - Outline
  • Definition
  • Development
  • Disadvantages

CMPT 355 Sept-Dec 2010 - w1d1

file based approach
File Based Approach

Definition

A file based system is

  • A collection of application programs that perform services for the end-users such as the production of reports. Each program defines and manages its own data.

Text p.7 Section 1.2.1

CMPT 355 Sept-Dec 2010 - w1d1

file based approach18
File Based Approach

Development

  • Typically developed
    • bottom-up
    • to meet the needs of a small group of users
    • often on local departmental systems
  • Evolution may be limited by initial design

CMPT 355 Sept-Dec 2010 - w1d1

file based approach19
File Based Approach

Disadvantages

  • Separation and isolation of data
    • Hard to link data in several files - limiting  data sharability
  • Duplication of data
    • Waste and inconsistency - due to  data redundancy
  • Data dependence
    • Program and data structures are highly interdependent - limiting  data evolvability
  • Incompatible file formats
    • Between programs and programming languages - further limiting  data sharability
  • No standard for queries
    • You have to develop you own queries - to get  data availability

CMPT 355 Sept-Dec 2010 - w1d1

database approach outline
Database Approach - Outline
  • Definitions
  • Advantages
  • Disadvantages

CMPT 355 Sept-Dec 2010 - w1d1

database approach
Database Approach

Definitions

A database is

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

Text p.14 Section 1.3.1

CMPT 355 Sept-Dec 2010 - w1d1

database approach22
Database Approach

Advantages

  • Data integrity
    • Ensuring the correctness, protection, and security of the data
  • Data sharability
    • Ensuring the ability to share data between applications and between users on a need-to-know basis
  • Data availability
    • Ensuring the ability to access the data when and where it is needed
  • Database evolvability
    • Ensuring that the database can be modified to meet changing needs
  • Avoiding redundancy
    • That occurs where multiple (often incompatible and inconsistently updated) copies of data are collected and used independently of one another

CMPT 355 Sept-Dec 2010 - w1d1

database approach23
Database Approach

Disadvantages

  • Complexity
    • Requires highly trained staff
    • Requires organizational infrastructure to handle costs, evolutionary planning, hardware and software support
  • Cost of (and Dependence on) DBMS
    • Large high performance DBMS have very high costs
    • Large high performance DBMS are closed source
  • Cost of Conversion
    • Interfacing with or ignoring legacy systems
  • Performance
    • Additions for new applications may slow down existing applications
  • High Impact of Failure
    • Moving from department threatening to organization threatening levels of risk

CMPT 355 Sept-Dec 2010 - w1d1

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