Transaction Processing in Mobile Environment

Computing Technologies are the technologies that are used to manage, process, and communicate data. In this article, we will learn about Transaction Processing in Mobile Computing. A transaction processing system allows application programmers to concentrate on writing code that will allow users to perform transactions simultaneously without bothering about what other users may be doing with their transactions at the same time:

• It manages the concurrent processing of transactions. 
• It enables the sharing of data. 
• It ensures the integrity of data. 

Issues in Transaction Processing

Database applications are normally structured into transactions. The transaction is a type of operation that makes sure that database does not change into an inconsistent state to disrupt the transactions.

One important aim in the design of any database system is to maximize the number of transactions that can be active at a time. DBMS ensures serializability using ACID constraints:

• Atomicity
• Consistency
• Isolation
• Durability

ACID properties have been redefined to support transactions in the mobile environment are: 

Atomicity Relaxation: Mobile Host is allowed to submit pieces of the transaction from different cells according to the movement. It requires the ability to break a transaction into many sub-transactions that can be concurrently executed. 

Consistency Relaxation: The database is logically partitioned into “clusters” based on some attributes. Data in the same cluster must be strictly consistent. Although the bounded degree of inconsistency is tolerated among the clusters.   

The above figure describes three clusters inside a bounded region.

Isolation Relaxation: The intermediate results of a transaction can be observed by other concurrent transactions. For example, if T1 is a transaction process and T2 is another transaction process then T1 should not be visible to T2. 

T1
	T2

T1 and T2 are two transaction processes where the operation of T1 is not seen by T2. 

Durability Relaxation: A disconnected Mobile Host can only commit a transaction locally if this transaction does not conflict with other transactions executed on the same HOST while HOST was disconnected. 

Transaction Processing Environment

1. Centralized Environment: Single user system executes all the transactions. 

2. Client Server Environment: Transaction and transaction initiation are done by the server and client respectively. Many clients can send transactions to servers simultaneously. 

3. Distributed Environment: Data is distributed over a network. The transaction can occur fully on a node or partially on a different node. 

4. Mobile Environment: Special type of distributed environment can accommodate user movements while processing transactions. 

Issues in Mobile Environment

• User Movement: Tracking users, and data recovery are complicated. LOG location determination is complex. 
• Disconnections: There may be temporary disconnections due to noise, fading of signal, handoff, etc. If there are planned disconnections, then the mobile user can perform some operations by downloading data beforehand. It can be referred to as data hoarding. Another way to deal with disconnection is by migrating transaction processing to a non-mobile computer. One more approach is maintaining proxy agents at MSS(Mobile Satellite Service). The process includes representing Mobile Host(MH) during its absence and participating in communication and finally handing over control to MH as it reappears.
• Poor Communication Media- Bandwidth allocated to mobile users could be very low. Interference from other traffic, noise, etc may corrupt data. MH tends to disconnect from the network whenever there is no data to send or receive in the near future. 
• Processing Power- With a less powerful CPU, database server operation is difficult.
• Memory- Memory availability is limited.
• Battery Power- Like memory, battery power is also limited.
• User Interface- It should be designed keeping in mind resource restrictions. 
• Security- Chances of data theft and unauthorized access increases while MH moves from one cell to another.