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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

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Introduction to databases l.jpg

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 l.jpg

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 l.jpg

    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 l.jpg

    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


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    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


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    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 l.jpg

    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 l.jpg

    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 l.jpg

    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 l.jpg

    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 l.jpg

    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


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    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


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    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


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    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


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    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


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    File Based Approach - Outline

    • Definition

    • Development

    • Disadvantages

    CMPT 355 Sept-Dec 2010 - w1d1


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    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


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    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


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    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


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    Database Approach - Outline

    • Definitions

    • Advantages

    • Disadvantages

    CMPT 355 Sept-Dec 2010 - w1d1


    Database approach l.jpg

    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


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    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


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    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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