Mark Dixon, SoCCE SOFT 131Page 1 23 – Entity-relationship diagrams

Mark Dixon, SoCCE SOFT 131Page 2 Session Aims & Objectives Aims –To introduce the main aspects of entity- relationship diagrams Objectives, by end of this week’s sessions, you should be able to: –create an entity-relationship diagram for a given database schema

Mark Dixon, SoCCE SOFT 131Page 3 People Database (with Hobbies) IDSurnameForenamesPhone 1DixonMark SmithJohn JonesSally BloggsFred AndersonGenny01752 HobbyIDDescriptionPersonID 1Archery1 2Herpetology1 3Music1 4Football2 5Rugby2 6Hitting people with swords1 Hobby Person

Mark Dixon, SoCCE SOFT 131Page 4 Entity-relationship diagrams Each table in db –stores details of entity shown as rectangular box Relationships between tables –represent relationships between entities shown as line between entities (boxes) PersonHobby

Mark Dixon, SoCCE SOFT 131Page 5 Relationship Types One-to-one One-to-many Many-to-one Many-to-many –(can't be implemented in relational database) ABABABAB

Mark Dixon, SoCCE SOFT 131Page 6 Which relationship type? IDSurnameForenamesPhone 1DixonMark SmithJohn JonesSally BloggsFred AndersonGenny01752 HobbyIDDescriptionPersonID 1Archery1 2Herpetology1 3Music1 4Football2 5Rugby2 6Hitting people with swords1 Hobby Person Hobby

Mark Dixon, SoCCE SOFT 131Page 7 Include files web pages –mix HTML, VB Script, and SQL can become messy use include files to –modularise (break up) code

Mark Dixon, SoCCE SOFT 131Page 8 Example 1: People.asp Personal Address Book Personal Address Book <% Const cs = " … … " Dim rs Set rs = CreateObject("ADODB.Recordset") rs.Open "Person", cs Do Until rs.EOF Response.Write rs.Fields("Surname").Value Response.Write " " rs.MoveNext Loop rs.Close Set rs = Nothing %>

Mark Dixon, SoCCE SOFT 131Page 9 People2.asp Personal Address Book Personal Address Book <% Const cs = " … … " Dim rs Set rs = CreateObject("ADODB.Recordset") rs.Open "Person", cs Do Until rs.EOF Response.Write rs.Fields("Surname").Value Response.Write " " rs.MoveNext Loop rs.Close Set rs = Nothing %> People.inc Example 2: People2.asp

Mark Dixon, SoCCE SOFT 131Page 10 Example 3: Procedures People3.asp Personal Address Book <!-- #include file ="People.inc" --> Personal Address Book <% ShowPeople %> People.inc <% Const cs = " … … " Sub ShowPeople () Dim rs Set rs = CreateObject("ADODB.Recordset") rs.Open "Person", cs Do Until rs.EOF Response.Write rs.Fields("Surname").Value Response.Write " " rs.MoveNext Loop rs.Close Set rs = Nothing End Sub %>