KS3, GCSE, A-Level Computing Resources
Manual methods of data capture
Data from forms that are filled out by hand often need to be typed in manually
Automated methods:
Once data has been collected, it can be transferred to a database. This can be done...
Electronic Data interchange (EDI) is the computer-to-computer exchange of documents such as purchase orders, invoices and shipping documents between two companies or business partners.
It replaces post, email or fax.
All documents must be in a standard format so that the computer can understand them.
EDI translation software may be used to translate the EDI format so the data can be input directly to a company database.
Once data has been collected and stored in a database, we will need effective ways to find and retrieve it.
SQL is a common query language used to retrieval and database management. MS Access Query by Example are another example.
A database management system (DBMS) is a software application that helps users store, organize, and access data. DBMSs are used in a wide variety of applications, including e-commerce websites, online banking systems, and social media platforms.
A DBMS serves as an interface between an end-user and a database, allowing users to create, read, update, and delete data in the database without dealing with underlying structure and complexities.
Information Gathered from IBM. Full website link here.
Transaction processing is a style of computing, typically performed by large server computers, that supports interactive applications.
In transaction processing, work (information processing) is divided into individual, indivisible operations, called transactions.
In the context of databases, a single logical operation is defined as a transaction.
ACID stands for Atomicity, Consistency, Isolation, Durability.
This is a set of properties to ensure that the integrity of the database is maintained under all circumstances. It guarantees that transactions are processed reliably.
This property requires that a transaction is processed in its entirety or not at all.
A change to the database is either completely performed or not at all. Half completed changes must not be saved back to the database.
This property ensures that no transaction can violate any of the defined validation rules.
Referential integrity, specified when the database is set up, will always be upheld. This means any change in the database must retain the overall state of the database.
The Isolation property ensures that concurrent execution of transactions leads to the same result as if transactions were processed one after the other. This is crucial in a multi-user database.
A transaction must not be interrupted by another transaction. The transaction must occur in isolation so other users or processes cannot access the data concerned.
A DBMS enforces isolation by implementing a system of recording locking.
This ensures that once a transaction has been committed, it will remain so, even in the event of a power cut or system failure.
As each part of a transaction is completed, it is held in a buffer on disk until all elements of the transaction are completed. Only then will the changes to the database tables be made.
What are potential problems with multi-user databases?
Allowing multiple users to simultaneously access a database could potentially cause one of the updates to be lost.
Example Situation:
Record locking prevents simultaneous access to objects in a database in order to prevent updates being lost or inconsistencies in the data arising.
Using record locking, a record is locked when a user retrieves it for editing or updating. Anyone else attempting to retrieve it is denied access until the transaction is completed or cancelled.
What are problems with record locking?
If two users are attempting to update two records, a situation can arise in which neither can proceed, known as deadlock.
Example Situation:
The Database Management System (DBMS) must prevent such situations (Deadlocks) from arising. Serialisation ensures that transactions do not overlap in time and therefore cannot interfere with each other or lead to updates being lost. An example of a serialisation technique would be Timestamp Ordering.
Timestamp Ordering:
In a database system, each object (such as a record or data entry) is associated with two timestamps: a read timestamp and a write timestamp. Here's how they work:
Consider a scenario where a user attempts to save an update to an object:
Many organisations cannot afford to have their computer systems go down for even a short time. Imagine the chaos if the air traffic control system goes down…
Organisations have built-in redundancy in their computer systems. Duplicate hardware, located in different geographical areas, mirrors every transaction that takes place on the main system.
If this fails, the backup system automatically takes over.
