Information System Design and Development What is an Information System? An information system involves the hardware, software used to collect, filter, process, create and distribute data. A key component in any information is a database. What is a database? A database is a collection of similar information which can be sorted and searched. Database Structure All the information in a database is known as the database file. Information on one particular thing in the database is a database record. Each of the individual pieces of information that make up a record are called fields. In many representations of a database, a file can be viewed as a table, where records are identifiable in the table rows and fields are the table columns. E.g. the school contains a file of all pupils attending. Each pupil has their own individual record. Within this record information such as their name, address and previous school are stored as records.

Field Types Each field in a database should be defined with a particular type, depending on the data to be stored in a field. The most common field types are: Text Number Date Time Graphics Calculated Link Boolean Choosing the wrong field type can provide problems at a later stage when performing sorts and searches in the database. Information System Design and Development

Field Types Each field in a database should be defined with a particular type, depending on the data to be stored in a field. The most common field types are: Text Number Date Time Graphics Calculated Link Boolean Choosing the wrong field type can provide problems at a later stage when performing sorts and searches in the database.

Flat File Databases A flat file database is where all the information in the database is stored in a single file (table). These are the types of databases you have used in the past. There are a number of problems in this approach. Consider the flat file database below: Puppy IDPuppy NameSexCostLitter IDDate of BirthSireDame 12RexM£500114/09/2013RoverSusie 15PrettyF£250114/09/2013RoverSusie 16PunchF£170223/10/2014SaulJudy 17JamieM£270223/10/2014SaulJudy Information, such as date of birth, sire and dame are needlessly stored many times. This is known as redundant or duplicate data. The more you write the same date, sire et. then the more possibility there is of making a spelling mistake, leading to data inconsistencies. Redundant data increases the storage space in a database (which can be significant if you have millions of records) and can lead to other problems in storing data efficiently. 114/09/2013RoverSusie 114/09/2013RoverSusie Information System Design and Development

To improve the efficiency of a flat file database, it is often a good idea to split the table into 2 (or more) related tables. This is called a relational database. In any relational database, (or even a flat file database) each table should have its own primary key. A primary key is a field (or fields) which acts as a unique identifier for each record in the database. Once a value appears in the primary key field in a record, then this value can never be used again in another record. Which field would act as the primary key in the database below? Information System Design and Development In the table, the litter ID is unique to a particular row (there are 3 rows in this table). Litter IDDate of BirthSireDamePuppy IDPuppy NameSexCost 114/09/2013RoverSusie Rex Pretty MFMF £500 £ /10/2014SaulJudy Punch Jamie FMFM £170 £ /10/2014PatchSasha20RexM£420 There may be 2 litters with the same date of birth, but they will not be confused because they cannot have the same litter ID.

To create a relational database, split the single table into 2 separate tables. What should the table below be split into? (Notice Litter ID is underlined to show that it is the primary key). Information System Design and Development Each litter contains details of one or more puppies. Relational Databases Litter IDDate of BirthSireDamePuppy IDPuppy NameSexCost 114/09/2013RoverSusie Rex Pretty MFMF £500 £ /10/2014SaulJudy Punch Jamie FMFM £170 £ /10/2014PatchSasha20RexM£ /09/2013RoverSusie Rex Pretty MFMF £500 £250 The 2 new tables will be about litters and puppies.

Information System Design and Development Relational Databases Litter IDDate of BirthSireDamePuppy IDPuppy NameSexCost 114/09/2013RoverSusie Rex Pretty MFMF £500 £ /10/2014SaulJudy Punch Jamie FMFM £170 £ /10/2014PatchSasha20RexM£420 Lets look at just the field names (and ignore the data): Splitting the litter data from the puppy data would leave the 2 tables as shown: (Puppy ID Puppy Name Sex Cost) (Litter ID Date of Birth Sire Dame) (Litter ID Date of Birth Sire Dame Puppy ID Puppy Name Sex Cost)

Information System Design and Development Relational Databases Litter IDDate of BirthSireDame 114/09/2013RoverSusie 223/10/2014SaulJudy 323/10/2014PatchSasha Problem: How do we now know which puppies are in which litter? When splitting the table, a copy of the primary key should be placed in the new table. (Puppy ID Puppy Name Sex Cost) (Litter ID Date of Birth Sire Dame) Puppy IDPuppy NameSexCost 12RexM£500 15PrettyF£250 16PunchF£170 17JamieF£270 20RexM£420

Information System Design and Development Relational Databases Litter IDDate of BirthSireDame 114/09/2013RoverSusie 223/10/2014SaulJudy 323/10/2014PatchSasha Problem: How do we now know which puppies are in which litter? When splitting the table, a copy of the primary key should be placed in the new table. (Puppy ID Puppy Name Sex Cost Litter ID) (Litter ID Date of Birth Sire Dame) Puppy IDPuppy NameSexCostLitter ID 12RexM£ PrettyF£ PunchF£ JamieF£ RexM£4203 Litter ID in the 2nd table is called a foreign key. A foreign key is a primary key in one table which appears in another table, to link the tables together.

Information System Design and Development Relational Databases Finally, the new table also needs a primary key. In this key, puppy ID is unique to each row in the table and so becomes the new primary key. Litter IDDate of BirthSireDame 114/09/2013RoverSusie 223/10/2014SaulJudy 323/10/2014PatchSasha (Puppy ID Puppy Name Sex Cost Litter ID) (Litter ID Date of Birth Sire Dame) Puppy IDPuppy NameSexCostLitter ID 12RexM£ PrettyF£ PunchF£ JamieF£ RexM£4203

Information System Design and Development Relational Databases Finally, the new table also needs a primary key. In this key, puppy ID is unique to each row in the table and so becomes the new primary key. Litter IDDate of BirthSireDame 114/09/2013RoverSusie 223/10/2014SaulJudy 323/10/2014PatchSasha (Litter ID Date of Birth Sire Dame) (Puppy ID Puppy Name Sex Cost Litter ID*) Puppy IDPuppy NameSexCostLitter ID 12RexM£ PrettyF£ PunchF£ JamieF£ RexM£4203 (Notice that Litter ID has an * to show that it is a foreign key in the 2nd table).

Information System Design and Development Relational Databases Review: What is an information system? What is a database? What are files, records and fields? What other terms are used to describe these parts of a database? What data types can fields take? What is a flat file database? What problems can occur in a flat file database? What is a relational database? What is the purpose of a primary key? What is the purpose of a foreign key? Lets put our relational database model on the computer.