The Research And Implementation Of Custom-built Interactive Interface Driven By Metadata

With the rapid development of computer network technology, theapplication of Internet not only limits into the information transmission, butalso had the widespread application in electronic government affairs,electronic commerce, and other fields. Browser/ Server pattern by itsconvenient becomes more and more popular. At present, many systems basedon B/S pattern use JSP (Java Server Pages) technology, but they all makepages partial dynamic displayed, such design make the system's flexibilityand reusability much lower. This article introduces the idea of metadata intodesign and development of dynamic pages which can be made by customer.We have done a lot in the research and the analysis to the design ofdynamic custom-made pages, and we realize our idea in the project, TheManagement Infrastructure for Projects of Sci. & Tech. of Jinlin Province(JL-MIP).In order to manages the electronic resources well, people proposed theconcept of metadata. Metadata is data about data. Or we can say metadata isdata which is more abstract. Concrete said, metadata is used in describing thedata's content, the cover scope, the quality, the management way, the dataowner, and so on. Metadata is the bridge between data and user. Metadata isalso widely used in the management of electronic resource, informationsearch from Internet, software development, and other fields.In the process of software development, sometimes half above codeduplicates the before similar system, so we can save development cost byenhancing the reusability of software. We can draw a conclusion that manyprocedures pieces are extremely similar after we carry on the analysis aboutthem. So we can reserve the same part while the different is taken place bysome specific structure data, which is metadata. The procedure will runaccording to metadata's explanation. In this way, different metadata isdeployed at different position in the procedure;we can get the same behavioras the original. Metadata is one kind of abstract to the procedure behavior.Metadata is highly abstract, as well as highly invariable. Procedure can runaccording to metadata's explanation, but metadata can't be modified by theprocedure.The design pattern of custom-made interface driven by metadata mayapply in electronic government affairs systems and electronic commercesystems which are based on JSP technology. To design the architecture, weuse metadata about data, metadata about interface and metadata aboutworkflow to describe the information of the system. We make the systemextensible, which can adapt the variety of data, user interface, and workflow.So the system's lifecycle is prolonged. The system mainly contains the datalayer, metadata layer, logic layer, and display layer.We have design three patterns of general display which containscompletely general pattern, demonstration template pattern and displayelement pattern. These three patterns have respective characteristic, andsometimes all of them should be used to work together. In completely generalpattern, system directly generates pages by metadata which is obtained fromthe dictionary in the database without any information about overallarrangement. The advantage of this pattern is that extra definition about pagelayout is not needed. But the disadvantage is that the pages generated areinvariable. To realize the entire page's general demonstration, sometimes wemust make the entire page into a special metadata, which is calleddemonstration template. That is a kind of metadata describe page layout. Indemonstration template pattern, system generates pages by demonstrationtemplate and other metadata. Custom-made pages are available by thispattern which we will mainly talk about. Every display element and otherrelative metadata is saved in the database according to the certain rule.System can generate pages after getting the information from the database bythe fixed algorithm. Custom-made pages are also available by this pattern,but the efficiency is very low, and much more storage has to be spent indatabase.The process user makes pages cannot be separate with general display.System generates metadata about pages according to the pages which isdesigned by user and save the metadata in the database. In the process ofgeneral display, system gets the metadata from the database, and generatesthe pages after doing some work to the metadata.The main part of the system adopt general display pattern because of itsadvantage such as that custom-made pages is available, light storage, highefficiency and so on. In this pattern, before the page is generated by thesystem, metadata about the page is obtained, including the parameter of thepage, the information of the workflow and the user's purview of the page.The system must make certain whether display the page for the user, and howto display. After that the page must be initialized, the function which cancheck whether the information user submit is validate must be defined. Theinformation about dynamic display must be obtained and then thedemonstration template must be loaded. There are controllers in the form inthe demonstration template because interactive action is needed. It's atechnical difficulty to encapsulate the data from the form submitted by user,and we must make it sure that the data encapsulated can be save in thedatabase correctly.The work of interface design module is to let users design pages throughthe browser by visual mode. Users can design the font , the format and thelayout of the pages which will be generate according to the demonstrationtemplate. In fact the pages users design just is the demonstration template. Torealize such function we should make use of the script of browser. Scriptlanguage usually has inner object through which event is relative withprocess, and the interactive action is available. The edit state of iframe isavailable in IE 5.0 and latter versions. The edit function through browserwhich we will develop is based on the edit function of iframe. The editfunction is mainly about inserting and editing words, inserting and editingtables, inserting image and inserting form controllers.The aim of the function of custom-made interface is to make the systemcan be design by users. Users can define workflows, as well as define thesteps of every workflow and the display of each step and so on. Such acustom-made system has high flexibility and reusability which can satisfiesthe different users with different need.When we finished the entire system, we found some deficiency. Themost serious one is that the share of metadata makes the independency ofmodules much lower. So the maintenance and the update of the systembecome difficult. We should do more to optimize the architecture of thesystem in the future.