You can define a database as a collection of data on one topic. It is organised in a way allowing to easily browse the information, make changes or add new items. Look at this diagram for one of the above examples: a simple phone book. A diagram of a phone number database A diagram of a phone number database The above picture shows a set of two contacts each of which is presented on a separate card. It appears that such a card can constitute a single row in a table: Contacts table Name Tel No. Joan 699 23 43 12 Adam 711 19 77 21 Terms and definitions: A single data which constitutes a part of a greater collection can be called a row or more professionally a record. The collection is normally called a table. Moreover, the most natural name for the table is one describing the data it offers/stores which is Contacts. Furthermore, each row in the table consists of columns often also called fields. In the table Contacts there are two columns (fields): Name and Tel No.. For simple uses a single table can make up a database. Many people consider these two equivalent. As you will see, for real databases we usually need more than one table. To sum up, you have already got a simple database with one table Contacts. It is very likely that you have already used spreadsheet applications like KSpread, OpenOffice.org Calc or Microsoft Excel. If so, you will probably wonder: since both spreadsheets and databases have tables, why should I use the latter? While comparing spreadsheets and databases you may encounter the following issues which you will later see in greater detail: Referential data integrity Data redundancy Data integrity and validity Limiting data view Performance and capacity Convenient data entry Reports Programming Multiuse Security Gradually exceeding the capacity of a mobile phone, expand your table Contacts adding a column (field) Address. Add more telephone numbers (office, home) for each person and add surnames to names. To make it simpler we assume the following: the table is limited to two people (obviously, there could be hundreds and thousands of them in a real database) there are no two persons with the same name and surname Contacts table Name and surname Tel Address Joan Smith 699 23 43 12 Western Gate 1, Warsaw Adam Willson 711 19 77 21 London, Frogs Drive 5 Joan Smith 110 98 98 00 Western Gate 1 Smith Joan 312 43 42 22 Warsaw, Western Gate 1 ADAM Willson 231 83 02 04 Frogs Drive 5, London Such a table can be made both in a spreadsheet and in a database. Using a spreadsheet is very easy, of couse. What problems do we encounter at this stage? Suppose you are using a spreadsheet and you need to change the address of at least one person. You have a small problem: you often have to change the address in many rows. For example, Joan takes three rows. A real problem will arise if you forget to change one of the rows - the address asigned to this person will be ambiguous, hence your data loses integrity. Moreover there is no simple way of deleting a chosen person from the table since you have to remember about deleting all rows releted to him or her. This is directly connected to the previous problem. In fields Name and surname and Address the same data is entered many times. This is typical of a spreadsheets' ineffective way of storing data because the database grows unnecessarily, thus requiring more computer resources (larger size of data and slower access). How can you solve these problems with a database? You can split information into smaller chunks by creating an additional table Persons with only two columns: Name and surname and Address: Persons table Name and surname Address Joan Smith Western Gate 1, Warsaw Adam Willson Frogs Drive 5, London Each row in the table Persons corresponds to a single person. Table Contacts is from now on a relation to the table Persons . Note the way data is entered in the fields Name and surname and Address. People entering data can be fallible, sometimes even negligent. In our sample data we have both different sequence of entering name and surname (Joan Smith and Smith Joan; Adam and ADAM) and many more ways of entering the same address. Surely you can think of many other ways. The above problem shows that ⪚ when searching the telephone number of a person whose address is "Western Gate 1, Warsaw" you will not get a full result. You will get only one row instead of three. Moreover You will also not find all the telephone numbers searching for the value "Joan Smith" in the field Name and surname, because "Smith Joan" will not fit to "Joan Smith". How can you solve these problems using a database? You can do this by changing the design of the table Persons by: Dividing data in the field Name and surname into two separate fields: Name and Surname. Dividing data in the field Address into three separate fields: Street, House number and City. Guaranteeing data correctness: by ensuring that no fields are empty, ⪚ you must always enter house number. A modified table looks something like this: Persons table Name Surname Street House number City Joan Smith Western Gate 1 Warsaw Adam Willson Frogs Drive 5 London Conditions required field required field required field required field required field Thanks to introducing the condition required field we can be sure that the entered data is complete. In case of other tables you may of course allow omitting certain fields while entering data. A spreadsheet displays all rows and columns of the table which is bothersome in case of very large data sheets. You may of course filter and sort rows in spreadsheets, however you must be extra careful while doing so. Spreadsheet users are in risk of forgetting that their data view has been filtered what can lead to mistakes. For example, while calculating sums you may think you have 100 rows of data while in fact there are 20 rows more hidden. If you want to work on a small subset of data, ⪚ to send it for others to edit, you can copy and paste it to another spreadsheet and after editing paste the changed data back to the main spreadsheet. Such "manual" editing may cause data loss or incorect calculations. To limit the data view database applications offer queries, forms and reports. A very practical way of limitting is the following extended version of the previously described table Persons: Persons table Name Surname Street House number City Income Joan Smith Western Gate 1 Warsaw 2300 Adam Willson Frogs Drive 5 London 1900 Let's assume that the newly introduced column Income contains confidential data. How can you share ⪚ contact details of the persons with your coworkers but without revealing their income? It is possible if you share only a query and not the whole table. The query could select all columns except for the column Income. In database world such a query is often known as a view. Your computer is probably quite fast, however you will easily see that it doesn't help with slow, large spreadsheets. Their low efficiency is first of all due to lack of indexes accelertaing the process of data search (databases do offer them). Moreover if you use things like system clipboard, even copying data may become troublesome with time. Spreadsheets containing large data sets may take ages to open. A spreadsheet loads lots of data to the computer's memory while opening. Most of the data loaded are probably useless/unneccessary for you at the moment. Databases unlike spreadsheets load data from computer storage only when needed. In most cases you will not have to worry how the database stores its data. This means that unlike spreadsheets, databases do not care about: The sequence of rows since you can order the rows according to your needs. Moreover, you can view the same data in many views with different orders. The same goes for columns (fields) of the table. Together with Limiting data view described in the previous paragraph these qualities constitute the advantage of databases. The latest editions of applications for creating spreadsheets enable you to design data-entry forms. Such forms are most useful if your data cannot be conveniently displayed in tabular view, ⪚ if the text occupies too many rows or if all the columns do not fit on the screen. In this case the very way the spreadsheet works is problematic. Fields for data entry are placed loosely within the spreadsheet and very often are not secure against the user's (intentional or accidental) intervention. Databases enable grouping, limiting and summing up data in a form of a report. Spreadsheets are usually printed in a form of small tables without fully automatic control over page divisions and the layout of fields. Applications for creating databases often contain full programming languages. Newer spreadsheets have this capability too, however calculations come down to modifying the spreadsheet's fields and simple data copying, regardless of the relevance and integrity rules mentioned in previous paragraphs. Data processing within a spreadsheet is usually done via a graphical user's interface which may slow down the data processing speed. Databases are capable of working in background, outside of graphical interfaces. It is hard to imagine a multiuse of one spreadsheet. Even if it is technically possible in the case of the latest applications, it requires a lot of discipline, attention and knowledge from the users, and these cannot be guaranteed. A classical way to sharing data saved in a spreadsheet with other person is to send a file as a whole (usually using e-mail) or providing a spreadsheet file in a computer network. This way of work is ineffective for larger groups of people - data that could be needed in a particular time may be currently locked by another person. On the other hand, databases have been designed mainly with multiuser access in mind. Even for the simplest version locking at a particular table row's level is possible, which enables easy sharing of table data. Securing a spreadsheet or its particular sections with a password is only symbolic activity. After providing a spreadsheet file in a computer network, every person being able to copy the file can try to break the password. It is sometimes not so hard as the password is stored in the same file as the spreadsheet. Features for edit locking or copy locking of a spreadsheet (or its part) is equally easy to break. Databases (except these saved in a file instead of a server) do not need to be available in a single file. You're accessing them using a computer network, usually by providing a user name and a password. You are gaining access only to these areas (tables, forms or even selected rows and columns) which were assigned to you by setting appropriate access rights. Access rights can affect ability of data editing or only data reading. If any data is not avaliable to you, it will not be even sent to your computer, so there is no possibility of making a copy of the data in such easy way as in case of spreadsheet files. Database design needs careful planning. Note that Contacts table redesign proposed in section 1.2 can generate problems when the table is filled with data. For example, renaming a field is a simple task, but splitting the Address field into separate fields requires careful and tedious work. To avoid such situations, rethink your database project before you create it in your computer, and before you and others will start to use it. Thus, by investing some time initially, you will most probably save your time on everyday use. Your needs are limited and your data will never grow to large volumes (can you actually forecast that now?) You are unable to acquire the methodology of database construction. You may however consider either outsourcing this task to someone else or using simpler tools. You use complicated spreadsheets and you lack time or money to switch to databases. Think or ask someone whether this does not lead down a blind alley. Don't count on magical tools that would change your spreadsheet (regardless how well made) into a database. Your data collection expands every week. You often create new spreadsheets, copy within these and you feel that this work is getting more and more tedious. In this case the effort of switching to databases easily pays off. You create reports and statements for which the table view of a spreadsheet is not suitable. You can then consider switch to using a database with form views. So far you have learnt the general characteristics of databases without going into much detail about specific applications for designing them. The first databases were built together with large mainframe computers in the 60s, ⪚ IBM System/360. Those were not the days of PCs, therefore these databases required a highly specialized personnel. Although the old computers' hardware was unreliable, they were immeasurably slower and had less storage capacity, one feature of databases still remains most attractive: the data access by many users through a network. In the 70s scientists formed the theory of relational databases (terms like: table, record, column (field) and relationality and many others). On the basis of this theory IBM DB2 and Oracle databases were created, which have been developed and used till today. In the late 70s the first PCs were constructed. Their users could (gradually) utilize many types of applications, including those for database construction. When it comes to large databases in companies, the situation hasn't changed: they still require powerful computers or computer complexes called clusters. This goes, however, beyond the topic of this manual. In the area of "accessible" databases with graphic user interface for PCs you can choose from the following: DBase - a tool for databases operation for DOS popular in the 80s. Files in DBase format are still used in some specific cases due to their simplicity. FoxPro - an application similar to DBase (early 90s). After being taken over by Microsoft, graphic user interfaces were introduced and therefore it is used for creating databases on PCs. This product is still offered, though seems a bit obsolete. Microsoft Access - an application for databases (data and graphic interface design) with many simplifications, therefore suitable for beginners, designed in the late 80s, based on 16-Bit Architecture. This product is offered and widely used till today, especially by small companies, where efficiency and multiuser requirements are not very demanding. FileMaker - popular application similar to MS Access in simplicity, operating on Windows and Macintosh platforms, offered since 1985. &kexi; - a multiplatform application (Unix/Linux, Windows, Mac OS X) designed in 2003, developed according to Open Source principles, part of the Trinity Desktop Environment project, &ie; graphic environment for Unix/Linux systems. A significant contributor to &kexi;'s development is the OpenOffice Poland company.