Mobile database
A mobile database is either a stationary database that can be connected to by a mobile computing device ( eg smartphone and PDA) over a mobile network OR
A database, which is actually stored by the mobile device this could be list of contacts, price information distance travelled or any other information
Many applications require the ability to download information from an information repository and operate on this information even when out of range or disconnected.
An EXAMPLE of this is your contacts and calendar on the phone. In this scenario a user would require access to update information from files in the home directories on a server or customer records from a database.
This type of access and work load generated by such users is different from the traditional workloads seen in client-server system of today
CONSIDERATION
• Mobile users must be able to work without a network connection due to poor or non existent connections. A cache could be maintained to hold recently accessed data and transactions so that they are not lost due to connection failure. Users might not require access to truly live data, only recently modified data, and uploading of changing might be deferred until reconnected
• Bandwidth must be conserved (a common requirement on wireless networks that charge per megabyte or data transferred)
• Mobile computing devices tend to have slower CPU and limited battery life
• Users with multiple device (eg. Smartphone and tablet) need to synchronize their devices to a centralized data store. This may require application specific automaton features
This is in database theory known as replication and good mobile database system should provide tools for automatic replication that takes into account that others may have modified the same data as you while you were away, and not just the last update is kept, but also supports merge of variants.
Users may change the location geographically and on the network. Usually dealing with this is left to the operating system, which is responsible for maintaining the wireless connection.
PRODUCTS
Commercially available mobile databases include those shown on this comparison chart
Name Developer Type Description
SQL anywhere Sybase iAnywhere Relational Embedded/portable database
Can synchronize with stationary database
DB2 Everyplace IBM Relational Portable, can synchronize with stationary database
SQL Server Compact Microsoft Relational Small- footprint
Embedded/ portable database for Microsoft windows mobile devices and desktops
Supports synchronization with Microsoft SQL Server
SQL Server Express Microsoft Relational Embedded database
Free download
Oracle database lite Oracle corporation Portable
Can synchronize with stationary database
SQLite D.Richard Hipp C programming library Public Domain
SQLBase Gupta Technologies LLC of Redwood shores California
Sparksee 5 mobile Sparsity Technologies Graph database Small footprint
Embedded/portable database for android, iOS and BB10
It allows traversal of nodes, minimum distance computations, community search etc
Couchbase Lite Couchbase Inc Document Oriented database A lightweight full featured embedded JSON document store
Supports iOS, android and REST SDK
Is sync ready using couchbase Syn gateway will sync and conflict resolution built in iBox DB IBoxDB Document oriented database Embedded transactional table style document database for android windows phone
Support mono Xamarin and Unity3D mobile development platforms
Realm Realm Inc Object database A lightweight full featured embedded object store
Support iOS and android

What is mobile database
Traditionally large scale commercial databases were developed as centralized database systems. However this trend changed as more and more distributed application started to emerge. The distributed database applications involved usually a strong central database and powerful network administration. However the newer technology trends have changed this paradigm because of the following technological trends:
• The notebook and laptop computers are being used increasingly among the business community
• The development and availability of a relatively low cost wireless digital communication infrastructure. This infrastructure is based on wireless local area networks, cellular digital packet networks, and other technologies
The rapid advancements of wireless communication technology and computer miniaturizing technology have enabled users to utilize computing resources anywhere in the computer network. For example you can even connect to your internet from an aero plane. Mobile database are the database that allows the development and deployment of database applications for handheld devices, thus enabling relational database based applications in hands of mobile workers. The database technology allows employees using handheld to link to their corporate networks, download data, work offline, and then connect to the network again to synchronize with the corporate database. For example with mobile database embedded in a handheld device a package delivery worker can collect signature after each delivery and send the information to corporate database at days end.
The current database systems do no provide special facilities for specific update operations in a mobile computing environment. Some of the commercially available mobile relational database systems are:
• IBM’s DB2 everywhere 1.0
• Oracle lite
• Sybase’s SQL
The databases work on palm top and hand held devices providing a local data store for the relational data acquired from enterprise SQL databases. The main constraints for such databases are relating to the size of the programs as the handheld devices have RAM oriented constraints. The commercially available mobile database systems allow wide variety of platforms and data sources. They also allows users with handheld to synchronize with open database connectivity (ODBC) database content, and personal information management data and email from Lotus Development’s Notes or Microsoft’s exchange. These database technologies support either query by example (QBE) or SQL statement.
Mobile computing has proved useful in many applications. Many business travelers are using laptop computers to enable them to work and to access data while travelling. Delivery services may use / are using mobile computers at the disasters sites, medical emergencies, etc to access information and to provide data pertaining to the situation. Newer applications of mobile computers are also emerging.
One of the issue relating to wireless computing is that creates a situation where machines no longer have fixed locations and network addresses. This may complicate query processing for the cases where location pays a key role, since it becomes difficult to determine the optimal location at which to materialize the result of a query. This may happen only for the cases where the location of the user is parameter of the query. For example if a traveler information system provides data on hotels, roadside services, e.t.c to motorist, queries about services that are ahead on the current route must be processed based on knowledge of the user’s location, direction of motion and speed
Another issue relating to mobile computing is the energy (battery power). It is a scarce resource for mobile computers. This limitation influences many aspects of system design. Can we reduce the requirements of data transfer for the sake of energy efficiency? Yes by doing scheduled data broadcast, we may reduce the need for mobile systems to transmit queries.
But on the other side it will increase the amount of data residing on machines administered by users, rather than by database administrators. In addition these machines may at times be disconnected from the network ; thus raising the question about the consistency of data
A MODEL OF MOBILE COMPUTING
The mobile computing environment consists of mobile computers which referred to as mobile hosts and a wired network of computers. The communication between the mobile hosts and the wired network takes place through the computers referred to as mobile support stations. A mobile support station manages the mobile hosts within its cell. But what is a cell? A cell is defined as the geographical area covered by a mobile support station. Mobile hosts may move between cells, thus necessitating a transfer of control from one mobile support station to another. Since mobile hosts may at times be powered down , a host may leave one cell and re materialize later at some distant cell therefore, moves between cells are not necessarily between adjacent cells. Within a small area, such as a building, mobile host may be connected by a wireless local area network within a small area, which may provide lower cost connectivity than a wide area cellular network. This will also reduce the overhead of transfer of control.
It is possible for mobile hosts to communicate directly without the intervention of a mobile support station. However such communication can occur only between the nearby hosts.
The size and the power limitations of many mobile computers have led to alternative memory hierarchies. Flash memories may be used in such systems to save power. If the mobile host includes a hard disk, the disk may be allowed to spin down when it is not in use, to save energy.
ROUTING AND QUERY PROCESSING
The mobile computing poses typical problems from the point of view of routing and query processing. For example as per the mobile computing model, the route between a pair of hosts may change over time, if one of the 2 hosts is mobile. The simple face may have a dramatic effect at the network level, since location based network addresses are no longer constants within the system. However these networking issues are beyond the scope of this course.
The mobile computing model also directly affects database query processing. In the case of distributed query processing the communication costs play important role in query optimization process while selecting the best method of query evaluation strategy. Mobility results in dynamically changing communication costs, therefore complicates the optimization process
Some anomalous factors which need to be considered for mobile computing are
• User time is a highly valuable commodity in most of the business applications.
• Connection time is the unit of monetaty charges is assigned in most cellular systems, therefore should be minimum
• Number of bytes or packets transferred is the unit of charges is computed in digital cellular systems
• Time of day based charges may vary based on whether communication occurs during peak or off peak periods
• Energy is limited often battery power is scarce resource and should be optimized
• One of the basic principles of radio communication is that it requires less energy to receive than to transmit radio signals. Thus transmission and reception of data impose different power demand on the mobile host
BROADCAST DATA
It is often desirable for frequently requested data to be broadcast in a continuous cycle by mobile support stations, rather than transmitted to mobile hosts on demand. A typical application of broadcast data is stock market price information. There are two reasons for using broadcast data:
• The mobile host does not have to invest on the energy cost for transmitting data requests
• The broadcast data can be received by a large number of mobile hosts in a single transmission, at no extra cost, thus, ensures effective utilization of the available transmission.
Thus, the mobile hosts need to only receive data as and when those data are transmitted, rather than consuming energy by transmitting a request. The mobile host may also have the local nonvolatile storage for storing (cache) the broadcast data as and when received, for possible later use. The mobile host may optimize energy costs by determining whether a given query may be processed using only cached data. In case the cached data is not found to be appropriate for the query, then the mobile host may, either may wait for the data to be broadcast, or transmit a request for data. However in order to make this decision, the mobile host must know when the relevant data will be broadcast.
The broadcasting of data may be made according to a fixed schedule or a changeable schedule. If the schedule of data transmission is fixed then the mobile host uses the known fixed schedule to determine when the relevant data will be transmitted. In the data transmission schedule is changeable then even the broadcast schedule may itself be broadcast as a well-known frequency and time intervals.
In effect, the broadcast medium can be thought of a disk with a high latency Request for data can be thought of as being serviced when the requested data are broadcast. The transmission schedules behave like indices on the disk. This area is still evolving and research is still being conducted on broadcast data issues
DISCONNECTIVITY AND CONSISTENCY
As one of the major cost involves in wireless communication, the connectivity cost, is paid for on the basis of connection time, there is an incentive for certain mobile hosts to be disconnected for substantial periods. However, during the time of disconnection, the user may still be working on the host machine and may issue queries and updates on data on locally cached data. This situation creates several problems of the following types:
• RECOVERABILITY
Updates entered at the mobile host machine which is not connected may be lost if the machine undergoes a major failure. This problem will result from the fact that only copy of information is kept at local host and simulation of storage that takes care of failure will be difficult to do.
• CONSISTENCY
The locally cached data may become inconsistent, but the mobile host can discover this fact only when it is reconnected. Similarly, the updates occurring in the mobile host cannot be propagated until reconnection occurs. However, such updates may be propagated as and when the mobile hosts reconnects. However if the mobile host caches read only copies of data, which is being updated by other computers, the cached data may become inconsistent once a different machine updates the value. In such cases on reconnection, the mobile host may be sent with invalidation reports that my inform it about inconsistent cache entries. In case updates can occur at both the mobile host and elsewhere, detecting conflicting updates become even more difficult. Details on these issues are beyond scope of this text.
SUMMARY
In this unit, we have discussed about the basic requirement of mobile databases. We have also dealt with the issues and problems faced in case of mobile database.

Definition
A mobile database is a database that resides on a mobile device such as a PDA, a smartphone, or a laptop. Such devices are often limited in resources such as memory, computing power, and battery power.
Key Points
Due to device limitations, a mobile database is often much smaller than its counterpart residing on servers and mainframes. A mobile database is managed by a Database Management System. Again, due to resource constraints, such a system often has limited functionality compared to a full blown database management system. For example, mobile databases are single user systems, and therefore a concurrency control mechanism is not required. Other DBMS components such as query processing and recovery may also be limited.
Queries to the mobile database are usually posed by the user of the mobile device. Updates of the database may originate from the user, or from a central server, or directly from the other mobile device. Updates from the server are communicated wirelessly. Such communication takes place either via a point to point connection between mobile devices (the client) and the server, or via broadcasting by the server. Direct updates from other mobile devices may use short range wireless communication protocols such as Bluetooth or Wi-Fi.

Reference https://webservices.ignou.ac.in/virtualcampus/adit/course/cst302/block2/cst302-bl2-u1.htm http://www.cs.uic.edu/~boxu/mp2p/mobile-databases.pdf