Problem Description
2.5 Classification of e-mail based information retrieval
According to the description of the previous sections, we conclude that the e-mail based information retrieval model is the best candidate for the resource-constraint mobile devices.
To utilize the e-mail by mobile devices to fetch the documents and to retrieve the information from the Internet or private local area network, according to the complexity of the model, we also divide them into three categories which are shown as follows:
Data-Driven System: All information retrieval functions are embedded in the main server. The user can only specify the interested data field, and then expects the corresponding results of those data fields returned from the remote server. In this type of e-mail based information retrieval system, the user has no flexibility to determine the control flow
of the information retrieval process. That is, the user only can specify some simple query commands with simple arguments to get the information from the server. There is no any control statements and other further advanced statements can be specified by the user.
Although such the system can provide the user having the ability to install their own program into the server to achieve their own information gathering purpose, in the client side, he only can just call the program with some simple arguments. He can’t specify the repeated execution times for some specified statements or programs, and he also can’t determine the control flow according to the return value of any program or application.
Control-Driven System: This type of e-mail-based information retrieval system is more flexible than data-driven system. It is supporting some kind of information retrieval script language. The user can utilize such script language to write some simple batch programs for retrieving information from the Internet. Moreover, the user can also operate the remote mobile agents by writing programs with this kind of language.
This type of e-mail based information retrieval system at least provides basic flow control statements, such as decision statements and loop statements, letting the user has more ability to control the execution flow of process of information retrieval. Furthermore, the well-formed results can also be treated as the reference for the next operational e-mail. The user can manage all of the functions and applications built in the system by writing a program in their operational e-mail. In most cases, this type of information retrieval is enough for mobile user to comprehensively fetch their interested information from the Internet.
Full Interactive System: In most cases, the Control-Driven System is enough for most mobile users. However, sometimes, if the system has not provide the user’s desired application, and there is no appropriate desktop PC for the user to install or deploy his own application, in such cases, the system also needs to provide the user the ability to install their own application into the remote server by his simple mobile device.
This is the main purpose of the invention of the Full Interactive System.
This type of e-mail based information retrieval system supports all the ability of programming language. Actually, it just extracts the program from the operational e-mail, and dispatches the extracted program into the operation system. After the execution of the program has been finished, the results will be wrapped into an e-mail, and then be sent back to the user’s mailbox. In this style, the user can write any customized mobile agent with this kind of programming language. For convenience of users, the programming language can be the traditional language such as C, JAVA, Perl, and any acceptable shell language etc.
In practice, the interpreter style language, such as Perl and some shell language, is easier to implement.
Different type of e-mail based information retrieval system has different characteristic and its applicable domain. The Data-Driven System is simple, and it is just for the user who only wants to query his simple interest information from the private database or some specified information sources on the Internet. Getting the item price of product of our company, getting the timetable of the school, or quoting the stock value from stock market are all the application examples which can be implemented by Data-Driven information retrieval system.
For more complex applications, such as surfing the Internet, or retrieving the information across many search engines, the Control-Driven information retrieval system is more viable than Data-Driven System since it provides more flexibility for the user to control the results from the server. In practice, the system will provide the control statements such as for/next, if/then, while/wend letting the user to control the execution flow for his information retrieval process. Furthermore, the system will also rearrange and reformat the results in a well-formed format, letting the user can directly utilize the results to retrieve the information from the Internet more intensive.
Sometimes, the simple control flow can’t fulfill all the requirements of the user. To support full function programming language is also important. The major advantage for an e-mail based information retrieval system is the great flexibility. In such system, the user can not only operate the remote application to obtain his interested information, but also write his own application by mobile device. Although the application is written on the mobile device,
the execution place is the remote server. Since the programming language can do everything that the computer can do, the user can do everything by his mobile device as well.