TPS - continued...

STORING AND RETRIEVING

A TPS requires an efficient method for storage and retrieval of data. Data is stored in a database or data warehouse.

DATABASE AND FILES

A database is an organised collection of data. An organisation stores all accounting and operational records in a database, often called an operational database. The data in an operational database is defined in a schema. Databases are designed using different structures:

- Hierarchical: organises data in a series of levels, using a top-down structure.

- Network: organises data as a series of nodes where a lower level node may have links to more than one higher level node.

- Relational: organises data using a series of related tables. Relationships are built between the tables to provide a flexible way of manipulating and combining data.

When designing a database for real-time transaction processing, the following features are important:

- Good data placement: when a large number of users are simultaneously using a database, the database should be designed to place frequently accessed data together.

- Short transaction: enables the entire transaction to be processed quickly.

- Real-time backup: needs to be scheduled during times of low activity to minimise effects on users.

- High normalisation: redundant information is kept to a minimum whenever possible to increase the speed of updates and improve concurrency.

- Archiving of historical data: data that is rarely referenced should be archived into separate databases or moved out of the heavily updated tables. This keeps tables as small as possible, improving backup times and query performance.

- Good hardware configuration: the hardware needs to be able to handle a large number of concurrent users and to provide quick response times.

A file is a block of data. In a database, a file is divided into a set of related records. The records contain the specific information, such as the details about a customer and a product. In a TPS there are five basic file types;

- Master file: contains information about an organisation’s business situation

- Transaction File: collection of transaction records

- Report File: data formatted for presentation to a user

- Work File: a temporary file in the system used during the processing

- Program File: contains instructions for processing the data

DATA WAREHOUSE

A data warehouse is a database that collects information from different data sources. Data gathered in real-time transactions can be used for analysis in an efficient manner if it is stored in a data warehouse. A data warehouse provides data that is:

- Consolidated: data is organised using consistent naming conventions, measurements, attributes and semantics. Semantics is the relationship of data within a database.

- Subject orientated: organises the key organisations data from operational sources so that it is available for analysis. Irrelevant data is ignored to make querying the data more efficient.

- Historical: real-time TPS represent the current value at any moment in time for various aspects of the business, such as stock inventory.

- Read-only: after data has been moved to the data warehouse successfully, it does not change unless the data was incorrect. The data stored in a data warehouse represents a particular point in time; it can never be updated.

BACKUP PROCEDURES

A breakdown in a TPS may stop the business. Well-designed backup and recovery procedures minimise disruptions when the TPS goes down. A backup is another copy of the data that could be used to rebuild the system. To cope with failures, the TPS must be able to detect and correct errors. The recovery of a database involves;

- Backup: periodic backup copies of the entire database typically produced once every day. The copy should be stored in a secure location where it is protected from loss or damage.

- Journals: journals maintain an audit trail of transactions and database changes. A transaction log records all the essential data for each transaction. A database change log contain the before and after copies of records that have been modified by transactions.

- Checkpoint: the DBMS periodically suspends all processing to synchronise the files and journals. All transactions and progress are completed, and the journal entries are updated. The system is then said to be in a “quiet state” where the database together with the transaction log is synchronised.

- Recovery manager: a program that restores the database to a correct condition and restores the transaction processing.

The two types of recovery are:
- Backward recovery: used to back out and undo unwanted changes to the database. Used to reverse changes made by the transactions that have been aborted.

- Forward recovery: starts with the backup copy of the database. It then reprocesses the transactions in the transaction journal that occurred between the time the backup was made and the present time.

Forward recovery is much faster and more accurate than backward recovery. Backward recovery involves the logic of reprocessing each transaction, and this is very time consuming.

Magnetic Tape

Magnetic tape is often used as a backup medium. It can store large quantities of data inexpensively. Magnetic tape is a very long, thin strip of plastic coated with a thin layer of magnetic material. This tape is often wound on two reels inside a cartridge. The main disadvantage of magnetic tape is that it uses sequential access to retrieve the data.

Grandfather – Father – Son

Is a backup procedure that refers to at least three generations of backup master files. The most recent backup being the “son”. This method is commonly used with magnetic tape for a batch TPS. If an error occurs during a batch run, then data is able to be restored using the backup. The “son” backup is one generation of the backup, if it is lost, destroyed or corrupted, it is necessary to go back one generation of backups, i.e. to the “father”.

Partial backups

When a full backup on a system is performed on one day, the next day’s data is not usually backed up as a full backup; instead there are partial (incremental) backups. This uses the master (previous full) backup as a reference and then only backs up any new files or files that had been changed from that point. In a TPS, these partial backs are known as journals, in the event of an accident, the data can be restored using the full backup and the journal files.

UPDATING IN A BATCH

There are two stages in batch processing; the first stage collects and stores the transaction data in a transaction file, and here it sorts the data into sequential order. The second stage is the processing of the data by updating the master file, this involves data additions, updates and deletions that need to happen in a certain order, if any errors occur then the entire batch is rejected. Updating in a batch involves sequential access.

UPDATING IN REAL TIME

It provides instant confirmation of a transaction. It involves a large number of users who are simultaneously performing transactions to change data. It increases the speed of data transmission and improvements in bandwidth have made real-time transaction processing possible. The person providing the information is typically available to help with error correction and receives confirmation of transaction completion. Data from real-time processing is accessed using direct or random access. Direct access occurs when the data is accessed without accessing previous data items; it is much faster than sequential access as previous data is not read.

OTHER INFORMATION PROCESSES

COLLECTING

Collecting data for a TPS involves generating the transaction data. E.g. people using an ATM generate transaction data by entering account details and typing requests on a keyboard. Collecting in TPS involves the use of hardware and a variety of forms.

Hardware

- MICR (Magnetic Ink Character Recognition): systems are widely used by banks to read account numbers on cheques. These numbers are printed using magnetic ink. MICR systems are designed to quickly and accurately read pre-recorded data on cheques and deposit slips.

- ATM (Automatic Teller Machine): is a banking terminal that performs common banking transactions, such as deposits and withdrawals. ATMs can be used at anytime, day or night, when people use ATMs, they are participants in a real-time TPS.

- Barcode readers: used extensively in retail industries to collect product information at point of sale (POS). Product information is stored on a central computer linked to the POS terminal. These are also used to keep track of stock movements.

Forms

A form is a document used to collect data from a person. When the form is completed, it is processed in batch or real time. There are many types of paper forms such as a sign on sheet for payroll. On-screen forms are created for computerised data entry purposes to populate fields in a database. The user can view, enter and change data in real-time. A transaction is completed when the suer completes the form. Forms can minimise data entry errors by automatically filling in previously stored data.

ANALYSING DATA

The results of processing TPS are stored in a database and are analysed in many ways to meet the information needs of the users. The output from the TPS is the input to other types of information systems, such as decision support systems and management information systems. A management information system is software which integrates database, spreadsheet and simulation functions to produce complex reports for management. Some common examples of MIS are reports on sale, stock inventory, payroll, orders and budgets.

ISSUES RELATED TO TPS

CHANGE OF NATURE OF WORK

Automation of jobs refers to the use of information technology to perform tasks once performed by people, such as POS terminals replacing people manually performing tasks. New technology has contributed to many of the changes in the workplace, such as workers learning new skills and completing ongoing training. This often results in fewer people being required to form the same task.

People from the environment have become the participants in TPS’s as they directly enter the transactions, for example an ATM machine has replaced the job that a bank teller would have performed to withdraw funds from a bank account. The internet also has allowed people to become participants in a range of TPS’s, e.g. people purchasing products online are bypassing the employees at the shop front.

NON-COMPUTER PROCEDURES

When a computer is unavailable in an organisation due to a breakdown, non-computer procedures are needed to deal with transactions in real-time.

BIAS

Data needs to be free from bias. Bias means that the data is unfairly skewed or gives too much weight to a particular result. The information process is carefully examined in many ways, however the data gathered in a TPS can be presented in biased ways using tables and charts.

IMPORTANCE OF DATA

Data security involves a series of safeguards to protect the data. Data is under threat of being stolen, destroyed or maliciously modified. There is a greater risk when the data is accessible to multiple users in real-time TPS. First line of defence is to only allow authorised users access to the data using passwords, personal objects and biometric devices. Further safeguards to protect data are:

- Encryption: the process of coding data while decryption is the process of changing it back. It is the most effective way to achieve data security during the transmission of data.

- Firewalls: used on networks to verify and authenticate all incoming data, it checks the password of anyone trying to access a network. On large systems, more than one firewall is necessary because barriers are needed to be placed at all critical points.

Data Accuracy is the extent to which it is free from errors. Data entered into a TPS is not always accurate, as errors can be caused by mistakes in gathering the data, mistakes in data entry, a mismatch of the data, out-of-date information, and the person entering the data.

Data Validation is used to check the entry of data. A well-designed TPS checks each transmission for easily detectable errors, such as missing data, data values that are too high or low, data values that are inconsistent with other data in the database and data in the wrong format.

Data Integrity describes the reliability of the data. It involves the accuracy, currency and relevance of the data. Data integrity in real-time TPS is provided when the transaction passes the ACID test.
- Atomicity occurs when all of the steps involved in a transaction are completed successfully as a group. If a step fails then no other step should be completed.

- Consistency occurs when a transaction successfully transforms the system and the database from one valid state to another.

- Isolation occurs if a transaction is processed concurrently with other transactions and still behaves as if it were the only transaction executing the system.

- Durability occurs if all the changes that a transaction makes to the database become permanent when the transaction is committed