Business computing Databases 2 4 january 2005

Program Create a simple database with several tables using Access Study a more complex database available for download on the Net omputing/session09_databases/ omputing/session09_databases/ bdcomptoir.mdb

Review of concepts Databases are tools to store, treat and retrieve STRUCTURED INFORMATION The business environment generates many sets of structured information –Accounting –Sales report –Production planning, production data –Human resources, etc.

Business and information In the business world we meet two types of information –Unstructured (or mildy structured) : presented in letters, reports, various documents, conversations –STRUCTURED (strongly structured) : information made of many elements, all of them with exactly the same shape. An element is called a RECORD

The various tools to deal with information and to communicate Word : the equivalent of a typewriter to produce pages of text Excel : a collection of cells organised into a grid, into which we make calculations. It is also used for clean presentation of tables PowerPoint : the equivalent of transparencies with synthetic points to communicate with an audience Access (a bit more complicated) : to store, treat, and retrieve (and create documents with) STRUCTURED INFORMATION In Access we must clearly distinguish in our minds STORING and RETRIEVING information

One table structured information Simple structured information is organised into a set of RECORDS, each of them with the same structure of FIELDS The collection of RECORDS is called a TABLE Think of a set of cards, bearing the same information on many people, and stored into a shoebox : –Record = Card –Field = an element of information on a card –Table = the collection of cards

A first example : a database of contacts We shall create a one table database of contacts, using (to start with) Excel On each record we shall have several fields : –Lastname –Firstname –Date of birth –Address –City –Department –Employer –Employer’s address –Salary –Picture

The records and the information in each field If we have 10 records (that is ten people in our contact list), this does not mean that we have 10 cities, and 10 employers We may have only 3 cities We may have only 4 employers After having created a unique table, we shall create a new database we several tables.

Excel When using Excel instead of cards in a box, the equivalent of the cards (that is the records) are ROWS The equivalent of fields are COLUMNS The whole Excel grid is the shoebox

Example Courtesy Lastnam eFirstnameAddressCity Departm entEmployerEmployer city MrsDupontMaryrue du marchéPoitiers86FuturoscopeChasseneuil MrDupontJohnrue du marchéPoitiers86ABCPoitiers MrDurandJacquesplace de l'égliseTours37Escem_ToursTours MrsDurandHélèneplace de l'égliseTours37FuturoscopeChasseneuil MsLaforêtSimonerue du MailPoitiers86Escem_PoitiersPoitiers MrDuboisPierreplace du marchéParis75DEFParis MrMartinHenrirue du MailPoitiers86FuturoscopeChasseneuil MrsMartinPaulinerue du MailPoitiers86Escem_PoitiersPoitiers MsMartinNancyplace de l'églisePoitiers86ABCPoitiers MrDutertreJackcours la reineParis75Escem_ToursTours

Comments on the example We have 10 central elements of information : the 10 people For each person, we have EXACTLY THE SAME 8 fields of elementary information –Name –Address, etc Some information is repeated : the cities, the employers, etc. (Poitiers -> 86 : so typing 86 each time is a repetition !)

Excel has simple database functionalities With our single excel table we can begin to implement databases functionalities Select all the data, and implement « data- >filter-> automatic filtering » Then we can display only the records corresponding to people living in Tours… It is called a (simple) REQUEST

The concept of REQUEST is central If our database was made of records, each of which is ONE SALE at some date, of some product, to some client, by such and such salesman, etc… …we could make a REQUEST to obtain the sales of last month, in the Northern sales region by our salesman John Doe, in the product range A

Usefulness of a database A sales database, as described, can provide very useful sales analyses to understand our market, our competitors, what we must correct, which clients we must visit more, etc. It is the beginning of information useful for business strategy An accounting system is also a database. It is one of the dashboards necessary to pilot a firm

Creation of the same database using Access First : we « analyse » our data, to see –What will be the « central elements » (the records) : here the solution is simple, it is going to be « the persons » –Which information is repeated several times ; it is going to go into different tables : here it is Cities Employers –These will be separate tables, beside the central « persons » table This « analysis » step is called : choosing the architecture of the database

Knowing how to type Knowing typing has always distinguished managers and secretaries A generation ago : –Secretaries knew how to type –and Manager didn’t Now this is still true, but the other way around.

Working with a database When constructing a database and filling it with data, life is not as intuitive as with Word or Excel, where we always « see » our data With Access we will often be disturbed by the question « but where the hell is the data ?! » It requires some practice to distinguish the data stored and the « things » displayed.

Table creation We have to create the tables – the equivalent of « shoeboxes » for some subset of the data There will be –a table for the cities –a table for the employers –and a main table for the persons We shall discover how this allows us to enter data without repetition

The table for cities The table for cities, in the « table display »

The table for cities The table for cities, in the « form display »

Table for employers Same procedures as for cities Define the structure (the fields) Define a primary key Fill in the data (either in a table display or in a form display)

Table persons Finally : the last central table : persons

Storage and display Now our database is filled in : But we wonder : « where is the data ? » It is inside the tables. But no table contains all the data

Table person Displayed as a form