P1, M1 and D1

What is a database?
A collection of organised information/data that is easily accessed at anytime to either gather receive information on something or to update a particular subject, this is what we call a database.

The main features of a database

• An Entity is data which is collected i.e. people, place etc.
• Throughout databases they have information that is stored about a certain individual or a certain which is known as a ''Records', these records are placed into tables and any individual piece of data on a person and thing which is known as a 'Field'. Obviously there is huge amounts of data that need to be stored, so we created tables to contain and organised.
• There are many versions of interfaces, i.e. Graphical, Speech and sound, Command, etc.They are a method that connects parts of the computer/network to allow communication. 
• Databases have multiple features to allow them to achieve certain goals or to make tasks much easier such as the import/export data between databases and applications- this features allows data to shared between databases or programs i.e. Microsoft® Excel. This allows for easy transfer between companies, if information needs to be moved.
• Integrated search- this feature is designed to search for particular data to be located and then accessed. It make it easier to locate information fast without scrolling endlessly or flicking through pages if database was paper based. 
• Permission and access- this feature is design to protect certain information from irrelevant changes. Access is granted by a permission Maintain control over your information by using permission-based access. Manage and assign privileges to add, modify and delete information.

Data types
Due to databases storing endless amounts of data, so that 'data types' were created to allow databases to be more efficient. there are many data types, some more common than others, so here a few.

• Text or Alphanumeric - is the storage of data that includes text, symbols and numbers. Examples of this storage would be 'names' i.e. John Smith, also 'postcodes' e.g. CV41 2RW are valid in this data type.
• Number or Numeric - obviously only stores numbers, either whole numbers, negative numbers or integers. Example of this data type can be measurements, shoe size, etc. 
• Currency - quite simply is the data type designed for the purpose of money (£25.50, $79.99) which can gross from little shops to huge company  
• Date /Time - is the storage of the time and the dates of the days of particular events, example 14/05/07 or 12:53. 
• Image - used for storing graphics images either bitmap or vector styled.
• All these data types are all designed to created organisation within a chaotic structure, thus making our job easier to mange and develop.

Relationship

The data that is split into 'sensible groups' which is then a separate tables for each group and once these tables are created, 'relationships' are then created to link them all together. this is known as relational database. The benefit of databases is that there is no duplication which makes the data storage much smaller and little room for mistakes.

Electronic vs paper

Obviously databases originated within a paper source which would contains peoples addresses that would be sorted by the person surname or by their birthday. This would be all held within a simple notebook, yet much larger databases (Yellow pages) would be organised by the career type. Whereas a computerized databases are generally found everywhere like search engines i.e. Google, Bing, etc, library databases, school electronic register all allow for easy and very fast search. Unlike paper based databases the electronic based allows a quick search, whereas you'd have to read through countless pages to find the tiny bit of data you wanted.

Interface
Interfaces are the navigation of databases, which consist of two meanings 'Telephones and Database'. But the database is the one to pay attention to. The switchboard is a menu button interface, to which once the button is pressed it'll carry out tasks. A switch is place/created (by the designer) once the database has been created, to allow standard commands to run. Interfaces allowed for access, design and search actions.But there bad points about them such as.

• Forums are spreadsheets that allows people to write comments, messages, etc. to each other. They can differ from either 'Public' that allows anyone from around the world to write on the page, whereas on a 'Private' that requires a 'Forum group' to read and write comments.
• Reports are easy to read data, that is done in a professional format.
• A poorly made interface will no operate correctly and will cause action to react slow.
• The constant screens you go through to get to the information that you need to get to.
• If the format is poorly done, it may be unreadable, either caused by font size or colour.
• Most of the bad thing are more formatting problems that can slow people down and bore them, but these can sorted very easily. Now the good points-
• They're very easy to use and get use to, even for a new comer.
• If appears difficult there are step by step options that guide you through the whole process. 
• They do not require a lot of power to operate.

From this we can gather that databases are easy to use set ups that can be used for long term use usually with out failure, even though some format difficulty's stall the user they are generally functional and tolerable.

M1

• A relational database relies on it primary keys that direct it to related records that are contained in different tables, for example the primary key will point to a record in one table and will also point to a record in another table. Both records are a compilation of information that are related to the primary key. 

Example 
Employee primary key- Employee number, that'll be linked to their salary (Pay table) and also to their address (Address table).

If the primary key doesn't direct you to the salary table entry, this means that the database has become broken. Referential integrity is a feature within the application that's makes sure the records exist in the tables so that'll allow the primary to point to them. 

• The field that allows every record to be identified uniquely is known as the 'Primary key'.

Example
All students throughout the UK all have a exam number that consists of 4 digits (2967). The same system applies here, as the number that has been allocated to you is unique and when it comes to marking your exams, your number is used to identify you. If this system wasn't applied the exam board may mix you up with another student with the same name. 
    

• The field within a table is known as a foreign key. In easy terms the foreign key links all the tables together after the primary key finds a relationship with the records. 

D1
To conclude this document is the common errors that can and have occurred within databases, to which we'll   explain what they are and how they can be avoided. 

• Let's start with incorrect data types. This error is caused generally by the 'Data entry clerks' as they possibly can enter an incorrect type of data i.e. wrong number, misspelled name, etc. This can be caused by the lack of 'Validation rules', these rules set a limit on the amount of characters/digits that can be entered or prevent a certain type of typing format to progress. So the ways to avoid wrong data types is to set validation rules to prevent any crippling mistakes, but the main way to stop this problem is for the data entry clerks to proof read all the data that they type.

• Following on from incorrect data types, renaming incorrectly follows the pattern identically, as they're generally the same mistakes so the same solution applies to solve i.e. validation rules and warning messages should prevent the wrong things being written. 

• One of the more common of the database errors to occur is the refusal of updating. This will normally happen whilst trying to insert new or update previous data, if your on a Access database. In quick terms you do not have the permission to write on the database. To overcome this problem and gain permission is to gain control over your server. 

• Null values are generally described as a unknown piece of data, yet a null value is not a zero or a string value. 

Example

Whilst filling out a page on a document and it asks you a certain question i.e. phone number, home town, etc. If you skip over that question and leave it blank that is a Null value. It a problem as it prevents certain data being collected. 

The ways to prevent this problem from occurring is to set validation rules, that'll stop people from skipping over the more important data types. Also to equip an error message on the validation rules as it'll inform people of what needs done and what is expected. 

• Validation is a problem is there's a lack of it, as fields can skipped, done wrong either by wrong characters and incorrect data entry. Without validation a database is in total disarray, data would be lost or not even entered in the database, so to avoid this chaos the rules should be created whilst in the creation stage of the database so that there is no problems occurring from the start.   

These where just some of these common issues that databases can and have happen throughout the creation of a database and over this time we've develop counter measures and techniques on these problem, so that  a database can remain running and effectively.