Civil War In Chad History Essay

Civil War In Chad History Essay After getting the independence from France in 1960, the north-central African nation of Chad has undergone four civil wars. These Chadian Civil Wars were against France, Libya, Sudan, Zaire/Congo, and the United States. . The current civil war is also connected to the neighbourers Sudan. Following are the civil wars that had been happened so far: 1.   First Chad Civil War (1965-1979) 2. Second Chad Civil War (1979-1982) 3. Third Chad Civil War (1998-2002) 4. Fourth Chad Civil War (2005-present)   First Chad Civil War (1965-1979) : The First Chadian Civil War started in 1965/66, with riots and insurgency against Chadian president Franà §ois Tombalbayes rule, known for its authoritarianism and distrust of democracy. By January 1962, Tombalbaye had banned all political parties except his own Chadian Progressive Party (PPT), and started immediately concentrating all power in his own hands. His treatment of opponents, real or imagined, was extremely harsh, filling the prisons with thousands of political prisoners. What was even worse was his constant discrimination against the central and northern regions of Chad, where the southern Chadian administrators came to be perceived as arrogant and incompetent. A long civil war began as a tax revolt in 1965 and soon set the Muslim north and east against the southern-led government. Even with the help of French combat forces, the Tombalbaye government was never able to quell the insurgency. Tombalbayes rule became more irrational and brutal, leading the military to carry out a coup on April 13, 1975 (in which Tombalbaye was killed), and to install Gen. Felix Malloum, a southerner, as head of state. In 1978, Malloum government was broadened to include more northerners. Internal dissent within the government led the northern prime minister, Hissà ¨ne Habrà ©, to send his forces against the national army in the capital city of NDjamena in February 1979. The resulting civil war amongst the 11 emergent factions was so widespread that it rendered the central government largely irrelevant. At that point, other African governments decided to intervene. Second Chad Civil War (1979-1982): The Translational Government of National Unity was coalition government of armed group that ruled Chad from the time period between 1979 to1982, during the most chaotic phase of the long running civil war which happened in 1965 to 1979.The GUNT replaced the fragile alliance led by Felix Malloum and Hissene Habre, which was collapsed in February 1979. The characteristics of the GUNT can be find out by the intense rivalries that led to armed confrontations and Libyan intervention in 1980. Libya intervenes in the support of the GUNT President Goukouni Oueddei against the former GUNT Defence Minister Hissà ¨ne Habrà ©. Because of international pressures and uneasy relations between Goukouni and Libyan leader Muammar al-Gaddafi, Goukouni asked the Libyans to leave Chad in November 1981; they were replaced by an Inter-African Force (IAF). The IAF showed itself unwilling to confront Habrà ©s militia, and on June 7, 1982, the GUNT was ousted by Habrà ©; Goukouni fled into exile. A series of four international conferences held first under Nigerian and then Organization of African Unity (OAU) sponsorship attempted to bring the Chadian factions together. At the fourth conference, held in Lagos, Nigeria, in August 1979, the Lagos accord was signed. This accord established a transitional government pending national elections. In November 1979, the National Union Transition Government (GUNT) was created with a mandate to govern for 18 months. Goukouni Oueddei, a northerner, was named President; Colonel Kamougue, a southerner, Vice President; and Habrà ©, Minister of Defense. This coalition proved fragile; in January 1980, fighting broke out again between Goukounis and Habrà ©s forces. With assistance from Libya, Goukouni regained control of the capital and other urban centers by years end. However, Goukounis January 1981 statement that Chad and Libya had agreed to work for the realization of complete unity between the two countries generated intense internationa l pressure and Goukounis subsequent call for the complete withdrawal of external forces. Libyas partial withdrawal to the Aozou Strip in northern Chad cleared the way for Habers forces to enter NDjamena in June. French troops and an OAU peacekeeping force of 3,500 Nigerian, Senegalese, and Zairian troops (partially funded by the United States) remained neutral during the conflict. Third Chad Civil War (1998-2002) The CSNPD, led by Kette Moise and other southern groups entered into a peace agreement with government forces in 1994, which later broke down. Two new groups, the Armed Forces for a Federal Republic (FARF) led by former Kette ally Laokein Barde and the Democratic Front for Renewal (FDR), and a reformulated MDD clashed with government forces from 1994 to 1995. Talks with political opponents in early 1996 did not go well, but Deby announced his intent to hold presidential elections in June. Deby won the countrys first multi-party presidential elections with support in the second round from opposition leader Kebzabo, defeating General Kamougue (leader of the 1975 coup against Tombalbaye). Debbys MPS party won 63 of 125 seats in the January 1997 legislative elections. International observers noted numerous serious irregularities in presidential and legislative election proceedings. By mid-1997 the government signed peace deals with FARF and the MDD leadership and succeeded in cutting off the groups from their rear bases in the Central African Republic and Cameroon. Agreements also were struck with rebels from the National Front of Chad (FNT) and Movement for Social Justice and Democracy in October 1997. However, peace was short-lived, as FARF rebels clashed with government soldiers, finally surrendering to government forces in May 1998. Barde was killed in the fighting, as were hundreds of other southerners, most civilians. Since October 1998, Chadian Movement for Justice and Democracy (MDJT) rebels, led by Yusuf Togoimi until his death in September 2002, have skirmished with government troops in the Tidbits region, resulting in hundreds of civilian, government, and rebel casualties, but little ground won or lost. No active armed opposition has emerged in other parts of Chad, although Kette Moise, following senior postings at the Ministry of Interior, mounted a small scale local operation near Moundou which was quickly and violently suppressed by government forces in late 2000. Deby, in the mid-1990s, gradually restored basic functions of government and entered into agreements with the World Bank and IMF to carry out substantial economic reforms. Oil exploitation in the southern Dobra region began in June 2000, with World Bank Board approval to finance a small portion of a project aimed at transport of Chadian crude through a 1000-km. buried pipeline through Cameroon to the Gulf of Guinea. The project establishes unique mechanisms for World Bank, private sector, government, and civil society collaboration to guarantee that future oil revenues benefit local populations and result in poverty alleviation. Success of the project will depend on intensive monitoring efforts to ensure that all parties keep their commitments. Debt relief was accorded to Chad in May 2001. Fourth Chad Civil War (2005-present): The current civil war in Chad began in December 2005. The conflict involved Chadian government forces and several Chadian rebel groups. These include the United Front for Democratic Change, United Forces for Development and Democracy, Gathering of Forces for Change and the National Accord of Chad. The conflict has also involved the Janjaweed, while Sudan allegedly supported the rebels, while Libya mediated in he conflict, as well as diplomats from other countries. In 2005, Chadian President Idriss Deby changed the constitution so that he could run for a third term in office, which sparked mass desertions from the army. The large-scale desertions from the army in 2004 and 2005, which forced Deby to disband his presidential guard and form a new elite military force, weakened the presidents position and encouraged the growth of armed opposition groups. The Rally for Democracy and Liberation (RDL) was formed in August 2005, and the Platform for Unity, Democracy and Change (SCUD), two months later, to overthrow the current government, accusing it of being corrupt and totalitarian. Later that year, the RDL and SCUD joined six other groups to form the United Front for Democracy and Change (FUCD).The situation was made worse by the alleged accumulation of oil wealth by Deby and his entourage. On 6 January 2006, Janjaweed militants crossed the border from Sudan into Chad and attacked the cities of Borota, Ade, and Moudaina. Nine civilians were killed a nd three were seriously injured.The Chadian government stated, The Sudanese militias attacked the settlements of Borota, Ade, Moudainayesterday killing nine and injuring three among the civilian population The Chadian government once again warns the Sudanese government against any hasty action because aggression by Sudanese militias will not go unpunished for much longer. In February 2007, a coalition of four rebel groups claimed to have taken the eastern border town of Adre. Chad rejected a plan to have U.N. troops along its eastern border. Victims from this attack were documented in the film Google Darfur. In March Former rebel Mahamat Nour Abdelkerim became defence minister. Government said Sudanese Janjaweed militia attacked and destroyed two villages in east Chad. On 26 October 2007, a peace agreement was signed between the government of Chad and four rebel groups: the Movement for Resistance and Change, the National Accord of Chad and two factions of the United Forces for Development and Democracy. In late November 2007, the rebel leader Mahamat Nouri accused Idriss Deby of ordering an attack on his fighters in the east of Chad. The army said on public radio there were several hundred dead and several injured among the Union of Forces for Democracy and Development (UFDD) fighters. Abakar Tollimi, secretary-general of the UFDD, disputed the army toll, saying only 17 rebels were killed. We have killed more than 100 from among the army ranks, he said after the clashes. On 30 November 2007, the UFDD declared a state of war against French and foreign military forces in an apparent warning to EUFOR Chad/CARà ¢Ã¢â€š ¬Ã… ½, comprising 3,700 European Union peacekeeping troops, who should deploy in eastern Chad on a U.N. mission to protect camps housing more than 400,000 Chadian and Sudanese refugees. Steps to be taken to stop the civil war in Chad: The main reason for the first civil war in Chad was the president of the Chad. He can stop those riots but he did not do so. Because he want all the power of Chad in his hand. First of all he should listen the need of the rebel groups. All the talk can be done by the violence but he did not do that. By spreading the violence it would be stopped. Efforts to end the war and resort to peace talks have been made, including by the U.S. government. There have been democratic advances, including the creation of a High Court and a Constitutional Court, the introduction of multi party elections and an increasingly free press. But Chad still remains highly divided along ethnic, cultural, political and regional lines and widespread repression by Debbys security forces continues.

Revenge In The Odyssey :: essays research papers

The Greeks, as portrayed by Homer, are a very vengeful people. Throughout The Odyssey, a theme of vengeance is dominant. These displays of retribution come from different entities for fairly different reasons. So why is revenge such a factor in The Odyssey? Fear and the overwhelming feeling of payback are two answers. Homer gives numerous examples of how certain characters demonstrate their power in a fury of rage. He writes of the payback Zeus gives to those who break the rules, of Poseidon’s hatred towards Odysseus, and of Odysseus’s revenge to those who have dishonored his home.   Ã‚  Ã‚  Ã‚  Ã‚  Zeus is the most powerful of all gods. All the Greeks with sense know not to cross him. A major practice in their culture is to invite in visitors that come to their doorsteps. This practice involves caring for the visitor by bathing and feeding them. After the visitor has been cared for, the host and visitor discuss the lineage of the visitor. This is done with the fear of Zeus and those who don’t follow the practice are dealt with. Those who don’t follow this practice are considered barbarians. Homer gives a clue into the extent of the fear when he writes that Telemakhos was “irked with himself / to think a visitor had been kept their waiting…'; (5). One example in The Odyssey is when Odysseus comes to the home of the Kyklops. Odysseus states:   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  “We will entreat you, great Sir, have a care   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  for the gods’ courtesy; Zeus will avenge the unoffending guest'; (153). Kyklops just answers that, “We Kyklopes care not for your thundering Zeus…';(153). This is a big mistake because directly after this statement, the Kyklops eats some of Odysseus’s men. Zeus does avenge the men through Odysseus. Odysseus gets the Kyklops drunk and stabs out his eye, allowing an escape. One thing that is bad for Odysseus, though, is the fact that Kyklops is the son of Poseidon, god of the earthquake. This now spurs a new challenge for Odysseus: he must get home with Poseidon’s obstacles.   Ã‚  Ã‚  Ã‚  Ã‚  Poseidon has never really liked Odysseus. When Odysseus tries to make it onto the shore of Skheria, Poseidon “…calls up wind / from every quarter, and sends a wall of rain…'; (89). Consequently, it is a safe assumption that Poseidon will really have it in for Odysseus. He states, “I thought he should suffer all the way [home]'; (233). After Odysseus returns home, Poseidon talks to Zeus and says he wants to put a mountain ring around the city and crush the ship of the Phaiakians.

Mobile Query and Processing in Mobile Database Environment

MOBILE QUERY AND PROCESSING IN MOBILE DATABASE ENVIRONMENT Agustinus Borgy Waluyo1 1 Bala Srinivasan1 David Taniar2 School of Computer Science and Software Engineering, Monash University, Australia {Agustinus. Borgy. Waluyo, Bala. Srinivasan}@infotech. monash. edu. au. 2 School of Business Systems, Monash University, Australia David. [email  protected] monash. edu. au Abstract Mobile database is a new context of database application in wireless environment. It introduces unique type of queries, and query-processing strategies that are different to traditional databases. We classify mobile database query into two categories, especially context-awareness query and adhoc query. Context-awareness query is further classified into location dependent, context dependent, and hybrid query. As for the query processing, we define three strategies namely mobile client, on air, and server strategy. Mobile client and on air strategy relates to caching strategy and broadcast strategy respectively. Finally, we include some challenges in mobile databases. 1. Introduction Recent advances in wireless technology have led to mobile computing, a new dimension in data communication and processing. Many predict a new emerging, gigantic market with millions of mobile users carrying small, battery-powered terminal equipped with wireless connection [1,2,10]. The mobile computing environment provides database applications with useful aspects of wireless technology, which is known as mobile databases. This advance technology has created a new age of nomadic database users. Basically, these users are simply accessing a database through a network. However, the network is now applied in wireless environment, and has several novel properties, which include user’s locations are constantly changing, the likelihood of losing connections is much greater than in a traditional network, and asymmetric communication environment in which the wireless bandwidth for uplink communication is smaller than downlink communication [11]. In general, mobile user communicates with a Mobile Base Station (MBS) to carry out any activities such as transaction and information retrieval. MBS has a wireless interface to establish communication with mobile client and it serves a large number of mobile users in a specific region called cell. In mobile environment architecture, each MBS is connected to a fixed network as illustrated in Figure 1(a). Mobile units or mobile clients in each cell can connect to the fixed network via wireless radio, wireless Local Area Network (LAN), wireless cellular, or satellite. Each of the wireless networks provides a different bandwidth capacity. However, the wireless bandwidth is too small as compared to the fixed network such as ATM (Asynchronous Transfer Mode) can provide speed up to 155Mbps [7]. 55 Wireless Network Mobile Base Station Mobile Base Station Wireless Network High speed Wired Network Fixed Host Fixed Host Crossing Crossing Mobile Client Query Query Processing Strategy Data Repository Query Result 2 Mobile Base Station Mobile Base Station Query Taxonomy = Mobile Client = Wireless Network 1 (a) Mobile Environment Architecture (b) Query Application in Mobile Environment Figure 1. Mobile Environment Architecture and Query Processing Figure 1(b) depicts the query processing in mobile databases. Mobile client initiates a query, and retrieve the data from data repository. The data repository is available in the fixed network. The query is transmitted through wireless channel, and the result is obtained using certain query processing strategies. As can be seen in Figure 1b, a sign of number 1, and 2, which is attached in query taxonomy, and query processing strategy respectively, correspond to the main content of this paper. Driven by differences between wired and wireless environment results in differences of type of queries, query processing mechanisms as well as communication technology. It is the aim of this paper to provide comprehensive query taxonomy, and processing strategy in mobile databases. Figure 2 shows a detailed structure of this paper. Subsequent sections in this paper are organized as follows. Section 2 describes query taxonomy in mobile databases. Section 3 contains the query processing strategies, and section 4 discusses some challenges in mobile databases. Finally, section 5 concludes the paper. In this paper, the term mobile client, mobile device, mobile user, user and client are used interchangeably Location D ependent Q ueries C ontext Aw areness Taxonomy C ontext D ependent Q ueries Hybrid Q ueries A d Hoc Q ueries M obile Q uery and Processing M obile C lient Processing Strategy O n Air Server Figure 2. Structure of Paper 56 2. Query Taxonomy In this section, we classify type of queries in mobile databases. The queries can be entirely new and specifically applied in the wireless environment, while the other can be a common type of query in traditional databases. 2. Context Awareness The word ‘context’ implies a variety of aspects. [14] defines the word context into three categories namely computing context, user context, and physical context. Computing context relates to computing resources such as network connectivity, bandwidth, printer, and workstations. User context associates with user’s needs, preferences, roles, profile, and alike. Physical co ntext involves environment issue, which include lighting, noise, traffic, temperature, and humidity. [5] adds another category of context called ‘time context’, which refers to time of a day, week, month, year, etc. 6] defines context as either the aspect of physical world or condition and activities in the virtual world. It is further described that context information can either be transient when the context associates with the environment at a point of time or persistent when the context involves a history of transient context. In simple words, we can always define that context relates to who, when, where, and what. Context awareness creates a new class of applications in mobile computing. With context awareness, mobile device is expected to adapt constantly in a wide range of dynamically and continually changing situations. It is important for the device to be able to aware of the situation, environment, and tasks that the mobile client is performing as well as will be performing in the near future. The utilisation of context information in an application minimises the amount of user involvement in a service by providing related information. Having known the context of the query enables the device to pre-fetch all data that is highly related and likely to be queried in the near future. With this query, client only initiates a single request and all related data will be retrieved implicitly. This technique avoids client to have multiple request that result in energy efficiency. Example: To find restaurants information in current region. The query will result of retrieving restaurants based on user’s preferences such as Italian, Chinese or fast food as well as pre-fetching maps, traffic and weather condition, which is likely to be queried next. Most applications have been focusing on location awareness rather than context awareness as a whole. Thus, we classify mobile database queries into location dependent queries, context dependent queries, and the combination thereof. 2. 1. Location Dependent Queries Location dependent query is a class of queries that are motivated by mobile clients. In this type of query, the location of the mobile client is a parameter of the query. The value of the location parameter can be provided by the client or a global positioning system (GPS). An example of this query is a traveler’s information system that provides information on hotels, restaurant, bars and the like, to motorists. Processing of queries must be based on knowledge of the user’s location. For queries services that are ahead of the current route, direction of motion and speed are necessary to be taken into account. Recent technology provides a new feature in automobiles, which offers 57 navigational aids as a built-in feature. In general, each location updates generate two direct costs, particularly transmission cost, which refers to the cost to inform the server of the new location, and server processing cost, which corresponds to the cost of updating the system containing the location of the mobile unit. The location parameter can be in any objects, such as taxis, trucks, and helicopters. This class of query can be further classified into two categories: (i) Continuous query, and (ii) On-demand query. Continuous query The continuous type of query includes real-time monitoring of mobile objects. This is different compared with conventional queries, which are based on an instant of the database at some moment in time. Real-time monitoring queries are continuous for monitoring purposes [3, 13]. Examples: (i) To request information about nearby tourist attractions, hotels, or shopping center while traveling. With this type of query, users only need to send a query once and notification of the updated information about nearby tourist attractions, hotels, or shopping center will be sent automatically as they move to different regions. ii) This query also helps tourists whenever they are close to a certain situation such as dangerous zone or traffic jam by providing some alerts to mobile user. Figure 3 shows an illustration of real-time query monitoring. In this application, the system must be able to provide the accurate query results and update them in real time whenever some mobile cl ients enters or exits the region defined by the query. This class of query can be referred as range-monitoring queries. The range-monitoring queries are removed from the system only when the user explicitly ends the query. Server End Query Query i Response i New Region Updated response i Region 1 Mobile Client 1 Moves to Region 2 Mobile Client 1 Figure 3. Continuous Query On demand query The on demand location dependent query is different from continuous query in a way that its database management does not manage the query but only the location of each mobile units in specified regions. Figure 4 illustrates on demand query. Every mobile unit is registered under one location server that manages the user profiles and is called the home location server. Location information of mobile clients can be stored at predefined sites like the user’s home location server in a network. Consequently, the search space for a user’s location can be reduced. However, when a mobile user crosses any boundaries of a cell, the information at the predefined site has to be updated accordingly. This type of query does not have to specify when to end the query since the server does not keep the query but the location [12]. Examples: To retrieve nearby hospital, police station or petrol station in the area. 58 Server Q uery i R esponse i Q uery j R esponse j Region 1 M obile C lien t 1 M oves to Region 2 M obile C lien t 1 Figure 4. On Demand Query When the parameter is an object, and mobile client requests an object that satisfies location criteria, then the situation becomes different. Figure 5 illustrates on demand query with location object parameter [8,15]. Examples: (i) Taxi operator wants to see how many free taxis are currently in a certain region. They can find free taxis and allocate them to another region that require more taxis or send them directly to the nearby customer. (ii) Tourists who come to the country, where there are no designated bus’ stops, nor timetable. They can utilize mobile device to retrieve incoming buses within a pre-defined time. Server Object Query Object Result Location Tracking Location Info Mobile Client Object Figure 5. On Demand Query with Location Object Parameter 2. 1. 2 Context Dependent Queries This type of query requires maintenance of an internal representation of user’s needs, preferences, roles, profile, etc. With these parameters, application will be able to decide the situation and task that a user is currently performing, and adapt to change of user needs and roles. This enables mobile device not to just retrieve the required information but also some other information that is highly relevant [6,8]. Examples: (i) Tourist wants to see list of restaurants in a town. Rather than retrieving the entire list of restaurants, the query retrieves the restaurants based on user’s preferences and need such as cuisine preference, price, occasion, etc. (ii) A business person wants to check the closest meeting schedule. The query retrieves the time as well as previous history of the meeting, people involved, client accounts, meal preferences, required data, etc. 9 2. 1. 3 Hybrid Queries Hybrid queries represent a combination of location dependent and context dependent queries. This type of query requires the system to maintain all parameters of context-awareness queries including location parameter. Examples: (i) A Traveler wants to find restaurants in the region that he/she will enjoy and within 10 minutes of current travel distance, (ii) A teenager wa nts to check movies in the nearby cinemas that he/she will like, and the show time can be met while considering current travel distance. These queries are very useful for nomadic users since it not only considers the users’ preferences and needs but also the location of the user. More sophisticated application utilizes a variety of sensors to monitor the environment as well as user’s action in order to provide assistance of the tasks being performed by the user. This application requires the ability to process data streams in real-time, analyze and interpret it precisely. The main point in context awareness query is to accurately analyze the environment and user’s intention, regardless of where the context information is obtained from. It is a difficult challenge since there is a possibility of conflicting data, and the need to have efficient processing to provide a useful application to the user. 2. 2 Ad Hoc Queries Ad Hoc queries are commonly utilised queries in traditional DBMS. This type of query explicitly mentions the required information in the query statement, and does not involve any context awareness information. Thus, the query result is only based on the actual query itself. Examples: (i) University student wants to retrieve his/her academic record or personal details. ii) Travelling sales person inquires about product availability, price, etc. 3. Query Processing Strategy We divide query-processing strategy for mobile databases into three parts, namely: (i) mobile/client strategy, (ii) on-air strategy and, (iii) server strategy. Mobile/clients strategy relates to how client manipulates and maintains the data in its cache efficiently and effectively. On-air strategy corresponds to data broadcasting stra tegies. With this strategy, the number of mobile users does not affect the query performance. Server strategy relates to designing techniques for the server to accommodate multiple requests so that the request can be processed as efficiently as possible. We claim that query processing for mobile databases is very much centered around the issues of caching, broadcasting, and scheduling. Figure 6 shows the architecture of query processing in mobile databases. 60 C Strategies lient OA n ir Strategies Server Strategies Figure 6. Query Processing in Mobile databases 3. 1 Mobile Client Strategy Mobile client’s strategy defines a number of strategies to maintain cached data items in clients’ local storage. As stated earlier, wireless communication channel in general suffers to narrow bandwidth while it is also inherently asymmetric communication, in which the downstream communication bandwidth from a server to the mobile client is much larger than the upstream communication bandwidth from clients back to server. Due to the above reason, caching of frequently accessed data items in a client’s local storage becomes important for enhancing the performance and data availability of data access queries. Another advantage of caching is the ability to handle fault tolerance. This is related to the characteristics of mobile computing in which each mobile client connects or disconnects from the network frequently. In some situation, the MBS may not be accessible due to problem like signal distortion. However, a query can still be partially processed from caches and at least some of the query results can be returned to the user [9]. Three main issues characterize a caching mechanism. These issues include caching granularity, caching coherence strategy, and caching replacement policy. Caching granularity relates to determining a physical form of cached data items. Caching coherence strategy or invalidation strategy involves cache invalidation and update schemes to invalidate and update an out-dated cached item [4]. Caching replacement policy is needed to retain the frequently accessed database items in a client’s local storage. The more effective a caching replacement policy in keeping the frequently accessed items, the better a query will perform and the more queries could be served during disconnection situation. 3. On Air Strategy In this scheme, the server periodically broadcasts the frequently accessed data items to clients through one or more broadcast channels, but the clients may not cache the data item of interest. This situation might occur when the client does not have enough memory or space to cache the required data. The behavior of this channel is unidirectional which means the server disseminates a set of data periodically, via this type of c hannel to a multiple number of users. A complete broadcast file is referred as a broadcast cycle. In this scheme, the client needs to listen to channel and filter the required data over the channel, which is also generally known as push-mechanism. Figure 7 shows on air query processing. 61 The advantage of broadcasting channel is its scalability. The number of users in the cell and the request rate do not affect the performance of the server. Thus, the utilization of bandwidth is better and the server workload is lower as compared with point to point/on-demand communication. Consequently, the power utilization of the client to retrieve information is also improved. However, it is very important to have good strategies to maintain the overall response time of the client to obtain information from the channel or else the advantages of data broadcast will be diminished. B ro ad cast C h an n el = listen in g to th e chan n el = retriev in g th e d esired data M o bile C lie nt Figure 7. On Air Query Processing 3. 3 Server Strategy This strategy considers the problem of pull-based broadcast scheduling where mobile clients send queries to the server through dedicated or point-to-point channel, server process the query, and send the result back to the client. The strategy concerns with broadcast and disk scheduling. Broadcast scheduling is to determine how queries to be served efficiently in the server considering a number of factors such as the length of the query, the wait time and the popularity of the items. Data scheduling is related to how data is placed on the disk that improves the query response time. The possibility of combining these two methods for query processing strategy is an interesting issue to be explored. B road cast server C ach e S erver D isk S erver T r a n sm itte r S erver Figure 8. Broadcast Server Architecture A database server is able to enhance the data retrieval performance by incorporating its own main memory and cache to store those database items frequently accessed by most mobile clients. Figure 62 8 shows architecture of broadcast server. A query can be processed either in the disk server or cache server. If the relevant data items have been retrieved earlier then the query is processed in the cache server. After processing a query, the results are transmitted to the transmitter queue, which subsequently send the data items through the wireless channel. 4. Challenges in Mobile Databases This section discusses some challenges in mobile database environment. The general concept that has been outlined in this paper contains an enormous issue to investigate. However, due to the limitation of page, only a few numbers can be mentioned. Location management is an important issue in mobile database research. Since the number of user population carrying mobile devices increases linearly with the service demand, the communication traffic for locating users also increases accordingly. This situation requires an efficient strategy for location tracking and management. Location management is a very essential factor in providing context awareness services. Context security introduces a new issue to be considered. Since context information may contain a very confidential and private data. It is necessary to ensure privacy issue protection for every user in a network. Caching management strategy, which includes caching granularity, caching coherent issue, and caching replacement strategy, requires a thorough investigation. A good caching management strategy is able to analyse, predict, and adapt to changing of user’s context in order to assist user in performing tasks. As for processing issue, data caching in mobile databases enable clients to obtain a high computing speed as server, by involving a much smaller data items volume. The asymmetric communication in mobile environment has made it a better reason to employ caching strategy. Broadcast scheduling is another issue to investigate. Generally, the more number of data to be broadcast, the more requests will be served from the data broadcast and this will reduce the chance of mobile clients to send the request to the server. However, at a certain point the advantage of the broadcast data will be diminished if there is too many data in the roadcast cycle. Consequently, it will severely affect the query response time since mobile users have to wait for considerably long delay before they receive the desired data. Therefore, it is essential to decide what data to be broadcast that serves most of the requests since the query access pattern is changed dynamically. 5. Conclusions Recent emergence of w ireless technology enables people to conduct activities, business, or transactions anywhere and anytime without any attachment to stationary computer like used to be. Nomadic people are now able to access email, news, weather, and query to the central database server using wireless devices. Mobile database focuses on the query issue that is the dominant operation in mobile computing. Since mobile database is a new dimension of database application, the type of query, query processing strategy, and communication technology that involves in the application are different than what applies in traditional databases. We have defined query taxonomy as well as query processing strategy in mobile databases. Query in mobile databases are categorized into context-awareness query and ad-hoc query. Context- 63 awareness query is further classified into location dependent, context dependent, and hybrid query. Query processing in mobile databases includes mobile client, on air, and server strategy. Mobile client and on air strategy corresponds to caching strategy and broadcast strategy respectively. Finally, we discuss a few challenges that open enormous opportunities for research in mobile databases. 6. References 1. 2. 3. 4. 5. 6. 7. 8. 9. ACHARYA S. , ALONSO R. , FRANKLIN M. AND ZDONIK S. 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