INFO 503Lecture #61 Introduction to Information Systems Analysis Database Design & Output Design...

INFO 503 Lecture #6 1

Introduction to InformationSystems Analysis

Database Design & Output Design

INFO 503

Glenn Booker


Database Design

• Information systems Create, Read, Update, and Delete data (CRUD)

• Data is stored in records which describe one instance of an entity (person, order, etc.)

• Each file contains many similar records

• A database contains collections of interrelated files


Conventional Files Pros & Cons

• Conventional (non-relational or flat) files are used in many legacy systems; e.g. Cobol and FileMaker Pro use them

• Fast and easy to develop

• Generally used for one specific application

• Results in duplication of data across files, causing maintenance and integrity risks

http://www.filemaker.com/


Relational Database Pros & Cons

• Provides more flexible format for storage

• Allows multiple applications to access data

• Slightly slower than conventional files, but improving

• Higher learning curve to overcome

• Manage using a database management system (DBMS)


Field Types

• A field is the smallest useful piece of data

• Four types:– Primary key - unique identifier– Alternate key - alternative to the primary key– Foreign key - links to a primary key elsewhere– Descriptive field – every attribute not a key!

• Every field should be used at least once


Records

• A record is round piece of bumpy vinyl which rotates on a turntable … oh, wait a minute *blush*

• A record is a collection of fields in a specific order or format

• Each record is generally fixed in length – Some systems can compress unused fields– COBOL can use variable length records


Records

• Records are read in units called blocks or pages– A block is sometimes called a physical page– The blocking factor describes how many

logical records are in each block– The blocking factor may be set manually for

performance reasons


Files and Tables

• A file contains all records of a particular structure

• A table is a relational database’s file

• There are many many kinds of files (see next slide)

• File organization and access may be tuned for performance enhancement


Types of Files

– Master files contain permanent information– Transaction files describe business events– Document files contain copies of historic data – Archival files contain master and transaction

file records offline which are no longer needed– Table look-up files contain static data for

reference calculations (tax tables, Zip codes)– Audit files record changes to other files


Data Architecture

• An organization’s data architecture includes – The files, databases, and database technology

used to store their data, and – The administrative structure used to manage the

data resources

• The architecture may include legacy information systems, local department databases, and shared data warehouses


Database Management

• Database administrators (DBA’s) try to plan, define, and structure this mess, so people can use it

• Database management systems (DBMS) are the tools used to create and manage a database– The heart of the DBMS is called the database

engine, which controls access to the data


SQL

• Structured Query Language (SQL) is used for both data definition (DDL) and manipulation (DML)– DDL creates and allows views of the data structures

– DML is used to access and use data from those structures (CRUD)

• SQL is used by nearly all relational databases – Oracle, DB2, SQL Server, Sybase, Informix, Access,

FoxPro, Paradox, dBase, etc.


Relational Database Tools

• A relational database models the data in a schema

• Tables can embed programs– Triggers are used to run programs based

on some event - e.g. updating records in another table

– Stored procedures are called by an application - e.g. validate new records before they’re stored


Data Modeling

• A good data model should be:– Simple, describing only one entity– Non-redundant, except for foreign keys– Flexible, for future improvement

• Normalization helps achieve all of these


Flat File Design

• Design of conventional flat files is dictated primarily by the output and input needs of a

particular application

• We won’t say any more, in order to discourage such barbaric practices :)


Database Design

• Detailed design of databases is heavily dependent on the DBMS used to implement them

• CASE tools can often generate SQL, based on the database model, which will even generate the tables and relationships needed

• Otherwise you have to do it manually


Database Design

• Each entity is implemented as a table– Primary and alternate (secondary) keys are

generally indexed, to make searches faster– Foreign keys are marked as such– Attributes become fields

• Supertypes and subtypes may not be implemented as such by CASE tools; may make them one table w/ stored procedures


Database Design

• Keys and other fields need to be defined in detail:– Data type (from list of allowable types in this

particular DBMS)– Field size (length or number of characters)– NULL allowable (no entry)

• Can’t allow NULL for a primary key

– Domain and default values


Integrity

• Integrity refers to knowing that the data is trustworthy, correct and can be predictably found

• Three kinds of integrity:– Key integrity– Domain integrity– Referential integrity


Key Integrity

• Key integrity can be achieved when every table has a unique, non-NULL primary key– Primary key must be non-NULL because

there must be an entry for every record

• If the DBMS does not directly support these features, then other controls must be taken to enforce them


Domain Integrity

• Domain integrity is achieved by ensuring every field is within its allowable domain (legal values)– e.g. don’t allow a 7-digit credit card number

• Note that this does not preclude incorrect values, only those values which are impossible


Referential Integrity

• Referential integrity is violated when a foreign key’s value does not match up to a primary key record

• To prevent this, must consider side effects of deleting any record which contains a foreign key– Might have to wait for all of a customer’s

invoices are deleted before deleting customer


Referential Integrity

• Rules for deletion should exist for every table to help maintain referential integrity– No restriction; delete freely– Delete:Cascade when you need to delete all

associated records from the foreign keys– Delete:Restrict when you hold off deleting

records until foreign key records are deleted– Delete:Set null when foreign keys are set null


Role Names

• Some organizations prefer to have all unique field names, to prevent confusion

• When naming foreign keys, each one can get a role name to distinguish its role differently from the primary key’s name– Primary key product_number in the Products

table may become foreign key ordered_product_number in the Orders table


Database Distribution

• Four options for database distribution:– Centralization; there is only one data server– Horiz. Distrib.; tables or records (rows) are

assigned different locations, but hard to analyze– Vert. Distrib.; attributes (columns) are assigned

different locations, also hard to analyze– Replication; duplicate entire tables at different

locations, but more complex and expensive


Database Capacity Planning

• The size of a database can be estimated by:– Record size: In a table, add the field sizes to get

the size of one record (one character=1 byte)– Table size: Multiple the record size by the

number of records expected in 3 yrs– Database size: Repeat first two steps for all

tables and add them up– Add a big factor for unexpected growth


The Database Future

• Object-oriented databases have become more common in the last few years– Some purely object-oriented databases are

available, but rarely used

• Since many organizations are heavily invested in relational databases (20+ years), object-relational databases are a popular hybrid transition technology (e.g. Oracle 9)


Output Design

• An information system generally has both internal and external outputs– Internal outputs are used for management of

the system and for reference by the users; they rarely leave the organization

– External outputs include any printed or displayed information which is used outside of the system and its organization


Internal Outputs

• Detailed reports are those which use little filtering to produce a comprehensive statement, such as all inventory on hand, or every transaction during some time period– Some detailed reports are historical or

regulatory in nature


Internal Outputs

• Summary reports provide a synopsis (maybe graphic) of the information, often for managers to look for trends or problems

• Exception reports describe when something

is wrong – outside of predefined limits (low stock)


External Outputs

• External outputs leave the system and its immediate users, generally to go to a vendor, customer, or external system– Might include invoices, paychecks, tickets,

passes, bills, purchase orders, etc.

• Turnaround outputs are external outputs which later become inputs for the same system (invoices returned by customer)


Output Media for Implementation

• Media used for outputs may include– Paper (preprinted or not)– Microfilm (?) – Magnetic media (e.g. CD-ROM, DVD, video)– Text files (e.g. append log entries)– Posted online (Internet or intranet)– Displayed on screen

• Client screen, projector, or POS terminal


Output Media for Implementation

• Consider different options; not just how you first think of the output being presented– Automated phone call to a pager or cell phone– E-mail messages– Multimedia (sound, pictures, video, etc.)

• Flash or Shockwave presentations

– Hyperlinks, or even entire web pages

http://www.macromedia.com/software/flash/

http://www.shockwave.com/


Output Media

• Printed output is often tabular and/or zoned– Tabular format looks like a table (rows and

columns of text data)– Zoned output is closer to a GUI input, or

the information at the top of a spreadsheet; collections of related data are grouped together

– Tabular and zoned output formats are often used together

• On-screen output may be graphic (charts)


Graphic Output

• Graphic output uses pictures to express information and help look for trends, but can’t replace narrative output to explain what is being shown– Need to be clear about the scope and source

of the data shown in a graph, so it is used appropriately by its audience

– Might have a hyperlink for definitions of the terms used


Graphic Output

• For every graphic output, need to consider– How often will the output be generated?– Does the output cover one moment in time or

many repeated assessments?– How many data points are to be displayed?– What medium will be used to present and

distribute the output? • A 32-bit color plot is really boring after it has been

re-copied in grayscale and faxed three times


Graphic Output – Chart Types

• Bar charts use horizontal bars, primarily for visual comparison rather than tracking

• Column charts use vertical bars to compare different items or track data over time

• Pie charts are good for showing a limited number of data points at one moment


Graphic Output – Chart Types

• Line charts show trends over time for one or more variables

• Scatter charts are used to compare two parameters to each other; often a correlation between them, or relationship, is sought

• Other types exist, but are used less often– Donut, area, radar, and control charts


Output Design Tools

• Printer spacing charts were used to design text-based outputs

• Now CASE tools and most database environments (Access, Crystal Reports, Oracle Designer) allow easy drag-and-drop layout of outputs

http://office.microsoft.com/home/office.aspx?assetid=FX01085791&CTT=6&Origin=ES790020011033

http://www.crystaldecisions.com/products/crystalreports/default.asp

http://otn.oracle.com/products/designer/index.html


Design Considerations

• Output should be easy to read and interpret– Every output should have a title– Every output should be date and time stamped– Section headings should be used to identify

groups of data– In forms, fields should be clearly labeled– Columns in tabular outputs need

column headings



– Legends should be used to explain column headings and field names

– Only required information should be shown (hide irrelevant details)

– Output should be usable in its presented form– Outputs should be balanced on the ‘page’– Users need to navigate easily and freely, or exit– Outputs shouldn’t have jargon, error messages



• Timing of output is very important; a beautiful report a week late is worthless

• Distribution of outputs must be complete enough to reach all relevant (affected) users

• Outputs must contain all information needed by its user - even if its requirements forgot something!


Output Design

• There are four steps to designing outputs1. Identify system outputs

2. Select physical output requirements

3. If needed, design preprinted external forms

4. Design, validate, and test the outputs (which includes obtaining feedback and refining the design)


1. Identify System Outputs

• Outputs should have been defined in the requirements for each design unit – in the DFD, look for data which leaves the system

• Content for each output should be defined in the data dictionary

• Consider the audience for each output, and when it will be generated (periodically and/or on an event-driven basis)


2. Select Physical Output Requirements

• Choose how the output will be presented based on its type and purpose, and on the feasibility limitations

• Pick the medium (paper, screen, kiosk, etc.)– Choose the output format (8.5 x 11” paper,

800 x 600 pixel screen, etc.)


2. Select Physical Output Requirements

• How often is this output generated? – Does its generation need to be scheduled?– Review the frequency the output will be needed

for the output volume requirements (amount of paper, number of forms)

– Is duplication needed? (Xerox, burn CDs)

• How will the output be distributed? How is that distribution controlled?


3. Design Preprinted Forms (opt.)

• Preprinted forms may need long lead time– What information will be preprinted?

• Will the form be mailed?

• What size will the form be? Perforated?

• How much volume of printing is expected?

• What legends and instructions need to be on the form? What colors will be needed?


4. Design, Validate, and Test the Outputs

• Key tabular report concerns– Page size, orientation, and headings– Report legend; column & row headings– Alignment and spacing of labels and headings– Data formatting, including field masks– Control breaks, make rows of data into sections– Clearly define the end of report


4. Design, Validate, and Test the Outputs

• Key screen (and web) report concerns– Size (screen resolution) and page size (kB)– Scrolling; can headings be frozen?– Navigation scroll bars, tabs, or buttons– Partitioning (zoning of data within a form)– Information Hiding; how do users get more info– Highlighting; how & when get user’s attention?– Printing; always provide an option to do so

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INFO 503Lecture #61 Introduction to Information Systems Analysis Database Design & Output Design...

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