SILS iSchool

20 April 2021

Value Added | daily

Class Schedule

Basics | sessions 01-03
  1. 19 Jan intro and clients | lecture | labs
  2. 26 Jan servers and command line | lecture | labs
  3. 02 Feb networks and protocols | lecture | labs
Web Development | sessions 04-08

  1. 09 Feb structural layer | lecture | labs
  2. 16 Feb presentational layer | lecture | labs
  3. 23 Feb using a structure | lecture | labs
  4. 02 Mar behavioral layer | lecture | labs
  5. 09 Mar design thoughts | lecture | labs
Dealing with Markup | sessions 09-10
  1. 16 Mar control objects and display | lecture | labs
  2. 23 Mar tools that read markup | lecture | labs
Working with data | sessions 11-14
  1. 30 Mar formulas, functions, vectors | lecture | labs
  2. 06 Apr data display | lecture | labs
  3. 13 Apr manipulate data sets | lecture | labs
  4. 20 Apr relational data bases | lecture | labs
Presentations | sessions 15-16
  1. 27 Apr designing a presentation | lecture | labs
  2. 04 May delivering a presentation | lecture | labs

Healthy, well-constructed entity classes are the foundations of an effective relational database.

Entity Classes

An entity class is the definition of the worksheets/tables that will store data, so they're essential building blocks of any database

A database should have a separate entity class/worksheet/table for every major component of the database

Data should not be unnecessarily duplicated in multiple entity classes/worksheets/tables

Duplicating data is a common error,
but it's easy to avoid if you structure your entity classes well

Each entity class table contains entities and attributes which are analogous to rows and columns in an Excel worksheet.
An entity set is a single table, analogous to an Excel worksheet.

Terminology Comparison
type ⇒⇒⇒⇒⇒⇒ ⇓⇓⇓⇓⇓⇓
ERModel entity set composed of entities which have attributes
Excel worksheets composed of rows which have column header cells

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An entity is a collection of facts about a particular person, event, or other item of interest
  • For example, in a library database, authors and their details might be an entity in an Authors entity class
  • Books and their information might be a entity in a Books entity class

Each row contains a record which is a single entry in a table and each record is composed of several descriptive fields.

Once you have entered entities into a worksheet/table, the collection of entities is an entity set

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Creating Entity Classes

When creating databases, sketch out the different entity classes/tables you will need and the data contained in the entity classes/tables before you begin

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Attribute data types

AutoNumber Automatically increments used for primary key (unique identifier)
Number integers that are negative or positive not numerals that do not have numeric values, like SSANs, PIDs, ZIP Codes, or telephone numbers
Text used for words or non-numeric-value numerals
Currency currency amounts with choice of decimal places
Date/Time Microsoft tools, like Excel and Access, store dates and times as a number representing the number of days since 01 January 1900, plus a fractional portion of a 24 hour day formatting is necessary to have the numbers display as dates and times

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Attribute Properties

all attribute types have properties - Some properties are primarily for text fields
Field Size number of characters
Format how the field's contents will be displayed
Decimal Places when data type is numeric
Default Value for new entries
Validation Rule range of acceptable entries checks values
Required a yes/no field indicates if a value is mandatory
Indexed creates an index for the field improves searching and sorting

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Setting Primary Keys

To distinguish one entity from another, entity sets contain a primary key attribute

the primary key is an identifier - such as a part number, a product code, or an employee ID - that is unique to each record

The primary key should be a piece of information that won't change frequently

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20 April lecture | preps | erm | entities | relationships | sql