Contents

THE PURPOSE OF RESEARCH WORK

The purpose of the given work is research in the field of designing the large distributed systems. For today there is a set of development in this area. These development also concern and the technologies based the Internet.

Dijkstra's shortest path algorithm

     Let's store the current minimal distance up to all nodes V (from the given top a) and on each step of algorithm to try to reduce this distance. let's originally establish distances up to all tops equal to infinity, and up to top а - null.

Let's consider performance of algorithm on an example. Let it is necessary to find distances from 1-st top up to all others. Circles designate tops, by lines - ways between them ("arch"). Above arches their "price" - length of a way is designated. Red the current shortest distance up to top is designated.

Step 1

     Initialization. Distances up to all tops the column V = ?. Distance up to а = 0. Any top the column is not processed.

Step 2

     We find such top (from yet not processed), the current shortest distance up to which is minimal. In our case it is top 1. We bypass all its neighbours and, if a way to the next top through 1 less than the current minimal way to this next top this new, shorter way as the current shortest distance up to the neighbour is remembered.

Step 3

     1-st tops first by turns the neighbour - 2-n top. The way up to it through 1-st top is equal to the shortest distance up to 1-st top + length of an arch between 1-st and 2-nd top, i.e. 0 + 7 = 7. It less the than current shortest distance up to 2-nd top, therefore new distance up to 2-nd top equally 7.

Steps 4, 5

     Similar operation it is made with two other neighbours of 1-st top - 3-rd and 6-th.

Step 6

     All neighbours of top 1 are checked up. The current minimal distance up to top 1 is considered final and to discussion is not subject (that it is valid so, Dijkstra) for the first time has proved. We shall delete it from the column to note this fact.

Шаг 7

     Practically there is a return to a step 2. Again we find the "nearest" raw (not deleted) top. It is top 2 with the current shortest distance up to it = 7.

And again we try to reduce distance up to all neighbours of 2-nd top, trying to pass in them through 2-nd. Neighbours of 2-nd top are 1, 3, 4.

     The first (under the order) the neighbour of top № 2 - 1-n top. But it is already processed (or is deleted - see a step 6). Therefore with 1-st top it is done nothing.

Step 8

     Another the neighbour of top 2 - top 4. If to go in it through 2-nd the way will be = the shortest distance up to 2-nd + distance between 2-nd and 4-th tops = 7 + 15 = 22. Time 22 < ?, We establish} distance up to top № 4 equal 22.

Step 9

     One more neighbour of top 2 - top 3. If to go in it through 2-nd the way will be = 7 + 10 = 17. But 17 > already known before distance up to top № 3 and equal 9, therefore the current distance up to 3-rd top we do not change.

Step 10

     All neighbours of top 2 are seen, we freeze distance up to it and we delete from the column.

Steps 11 - 15

     Under already "fulfilled" circuit we repeat steps 2 - 6. Now "close" appears top № 3. After its "processing" we shall receive such results:

The further steps

     We make the same with the staying tops (№ under the order: 6, 4 and 5).

Completion of algorithm

     The algorithm finishes work when all tops are deleted. The result of its work is seen in last figure: the shortest way from 1-st top up to 2-nd makes 7, up to 3-rd - 9, up to 4-th - 21, up to 5-th - 20, up to 6-th - 11 standard units.

ТЕХНОЛОГИЯ WEB SERVICES

The network the Internet became the conventional factor of a business and public life. Wide prevalence and the increased throughput create conditions at which it is favourable to solve many problems by means of Internet - technologies. However the Internet unites in itself many various platforms, and the information contains in various sources of the data. Therefore the problem of connection of such diverse data, and also creations of a way which allows to receive them as convenient for the further processing is actual. The concept of webs - services (Web Services) is called to solve this problem{task} of association, integration of diverse systems on the basis of open standards. The given work is devoted to webs - services, in it{her} substantive provisions of model of webs - services, and also components of this model and the technologies used for their realization are briefly considered. The practical part of work contains the small example showing development of web - service and appendices using it. The example is based on realization of the concept of webs - services within the framework of Java-technologies. For understanding of an example enough base knowledge Java. Webs - services are the concept of creation of such appendices which function can use the Internet by means of standard reports. Now this concept apply and develop many leading companies in IT-area. The concept of webs - services is realized by means of lines of technologies which are standardized World Wide Web Consortium (W3C). The interrelation of these technologies can be presented conditionally as follows.

     Webs - services are one of variants of realization of componental architecture. XML is the base to creation of the majority of the technologies connected to webs - services. For the removed interaction with webs - services it is used Simple Object Access Protocol (SOAP) [3.] SOAP provides interaction of the distributed systems, irrespective of objective model, operational system or the programming language. The data are transferred as special XML documents of a special format. According to definition W3C, webs - services it is applications which are accessible under reports which are standard for the Internet. There is no requirement that webs - services used any certain transport report. Specification SOAP defines, how messages SOAP and the transport report communicate. Most frequently transfer SOAP of messages under report HTTP is realized. Also use is widely distributed as transport report SMTP, FTP, TCP. According to definition W3C, " WSDL - format XML for the description of network services as set of the final operations working by means of messages, containing document-oriented or procedure-oriented the information " [3]. Document WSDL completely describes the interface of web - service with an external world. It{he} gives the information on services which can be received, having taken advantage of methods of service, and ways of the reference{manipulation} to these methods. Technology Universal Description, Discovery and Integration (UDDI) assumes conducting the registry of webs - services. Having connected to this registry, the consumer can find webs - services which in the best way satisfy to its requirements. Technology UDDI enables search and the publication of the necessary service, both the person, and the program - client. Search and the publication in the registry is given the program - client as a set of webs - services of registry UDDI. Webs - services are positioned as the software of an intermediate layer. Use webs - services can as the client applications directly working with the user, and other applications (including other webs - services). Webs - services are placed on servers of applications. Developers of the concept of webs - services offer the following scripts of application of webs - services: Webs - services as realization of logic of the application (business - logic). That is, creation of the new application business - logic which is realized in web - service.

Webs - services as an integration tool. That is, use of web - service as way of access of the removed clients to internal IS the companies, or for the organization of interaction of a component (for example, EJB, a COM-component) with the various removed clients.

Creation of alternative service. In this case, by development of new web - service the description of the interface of already existing web - service is used. Thus, service has many potential clients at once from the moment of the beginning of work, and connection to it{him} does not demand essential changes on the side of the client. As it has been told above, the concept of webs - services includes an opportunity of conducting the registry of webs - services. The description of the interface can be received from such registry. After creation and introduction of new web - service, it is meaningful to register it in the registry. Then clients by search of the services realizing the initial interface, will receive the instruction and on new web - service. Use of web - service as building block at creation of the application. The application can use webs - services as the removed components which give the certain functionality. There are various services which give the qualitative decision of such problems as identification, conducting a calendar, sending of messages, search, translation, etc.

Besides other variants of use of webs - services are possible. For example, there are researches on use of webs - services for construction of the distributed computing and information systems and peer-to-peer and with complex hierarchical structure.

4. STRUCTURE OF THE DISTRIBUTED SYSTEM

The structure of the distributed network is submitted on fig. 4.1. It will consist of a server and client part. It is important to note, that the Web-server does not work directly with storehouse of the data and does not realize logic of system. These functions are concentrated in Web-service which is offered by our system. All clients based on HTML or WML the interface, work with the Web-server while for all other clients Web-service is given. Thus even the internal web-server of our system is the client for Web-service.

For sites of the distributed system the following products of various firms - manufacturers of large corporate systems are chosen:

5. DATABASE

The circuit of a database is submitted in figure 5.1. It describes a principle of construction of the circuit of a database at a conceptual level. At a physical level it will be used DBMS Oracle and accordingly types of the data will correspond to those which are used in DBMS. Basically due to following innovations Oracle has won today huge popularity in market DBMS:

Figure 5.1 - Circuit of the given DB

Figure 5.2 - Section of market DBMS for platform UNIX

Figure 5.3 - Section of market DBMS for platform WINDOWS

6. CONCLUSIONS

     The given research shows, that the task in view assumes presence of well thought over architecture of the distributed network, and also well thought over algorithm of search of the shortest way on the column., the analysis of speed of algorithms is necessary for optimization of work of the program that assumes conducting detailed statistics of work of all services.

     All data should be stored in a DB, and for work with them it is necessary to use classes controlled by the controller. Business methods should work directly with these classes, instead of with DBMS. Also, as well as the Web-server should work with Web-service, instead of from a DB.

     As above the project 2 programmers it is necessary to use patterns of designing at a spelling of a code which will be an intermediate link between them work. The pattern Abstract factory is the most suitable as it allows to share the interface and realization of the module of work with columns, giving the programmer who uses the given module, dynamically to receive copies of concrete classes of realization of library. It in turn will allow to create some realizations of library of work with columns and dynamically them to change in an operating time of system.

PS:At the moment of creation of this page the project is at a stage of development. The full text of masters work will be accessible after protection in 2007.