Databases

Databases

1. A database is a persistent organised store on a computer system

2. Databases need to be: accurate, up to data, available to those who need to use them,protected from those who shouldn't have access .

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3. Data can be lost because of: a catastrophe, such as fire or blood an accident, such as an employee deleting data malicious action, such as by an intruder

4. Data is protected against loss by: making regular back ups having a mirror database server so that data is saved in at least two places storing back ups in a safe place such as in the cloud or otherwise off site restricting access keeping audit trails of who has accessed data

5. Data integrity can be maximised by: suitable validation software that prevents inconsistent states

6. Validation is the process of checking data when it is input. Validation is carried out by software, not by humans.

7. Verification is checking that the data entered is correct. It can be a simple visual check against the source data or an algorithm checks two copies, entered independently, and flags up inconsistencies.

8. The simplest model is a flat file database. This is just rows and columns such as would be suitable for an address book. Each row is called a record and each column is called a field. Flat file databases are very limited. One of the main problems is that data might be repeated unnecessarily

9. A hierarchical database is useful when making an inventory,the data is organized into a tree-like structure. The data is stored as records which are connected to one another through links.

10. Relational databases are the most useful model and consequently the most common type of database. They are far more flexible than other models and can replace other models in most cases.

11. A DBMS is a database management system. This is software that looks after a database at a fundamental level. It is general-purpose tool that allow database administrators to: create database applications protect data run queries to extract data keep data consistent keep data accurate

12. When a change takes place in a database, it is called a transaction. Transactions must not damage the integrity of a database.

13. Most DBMSs use record locking. This means that if one user has opened a record for writing (editing), other users can only view it until the transaction is committed. Then it is unlocked for other users.

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