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Interactive Memex - INTRODUCTION, RELATED WORK, Petri Net, Memex, Some Powerful Bookmarks, Bookmark Organizers, and Other Works

web site token trail

Sheng-Uei Guan
National University of Singapore, Singapore

INTRODUCTION

With the development of the Internet, a great deal of information is on-line. Popular search sites could be visited million times daily and the sites related to your interest will often be visited by you. Although bookmarks can be used to record frequented Web sites, browsers discard most history and trail information. The explosion of information needs a more effective mechanism. Memex has been considered in this domain. Assisted by Memex, a Web surfer can retrieve the URL trails that a user visited several months ago. In this paper, we propose a mechanism Self-modifiable Color Petri Net - SCPN to simulate the Memex functions in a Web browser. In this mechanism, an SCPN instance is used to record a trail of a topic, a place in an SCPN instance represents a Web site.

RELATED WORK

Petri Net

Petri Net is a graphical notation for the formal description of systems whose dynamics are characterized by concurrency, synchronization, mutual exclusion, and other conflict, which are typical features of distributed environment. A formal definition of Petri Nets is a four-tuple (P, T, I, O) (Peterson, 1981) where P is a set of places that are the state variables of a system; T is a set of transitions, which are state changing operators. I and O are the pre- and post-conditions of a transition. The dynamic performance of a Petri Net is controlled by the firing rule.

Several extended Petri Net models have been proposed to extend its application domains. Examples of which are Object Composition Petri Net (OCPN) in (Little, 1990) and Enhanced Prioritized Petri Net (EP-net) in (Guan, 1999) and (Guan, 2002) which is an enhanced version of P-net in (Guan, 1998). The general concepts of Petri Net are described in the next section. Self-modifiable Color Petri Net (SCPN) is also introduced in the next section.

Memex

As early as 1945, Vannevar Bush proposed a desktop personal information machine called the Memex (memory extender) (Bush, 1945). Memex focused on the problems of “locating relevant information in the published records and recording how that information is intellectually connected”. An important feature of Memex is the function of associative indexing that presents the feature of hyperlinks. In addition to these links, Bush also wanted Memex to support the building of trails through the material in the form of a set of links that would combine information of relevance for a specific topic.

Some Powerful Bookmarks, Bookmark Organizers, and Other Works

There are quite a number of powerful bookmarks and organizers developed like the Personal Web Map (PWM) (Yamada, 1999), Bookmark Organizer (Maarek, 1996), PowerBookmarks (Li, 1999), and CZWeb (Fisher, 1997). All of these provide organization and management of bookmarks but not Memex functions, that is, they do not provide surfing history and trails.

A related work which uses trails is Memoir (Derource, 2001). Trails are used to open hypermedia link services and a set of software agents to assist users in accessing and navigating vast amounts of information in Intranet environments. The trails in Memoir are mainly used to record actions on documents that users have visited. In our Memex application, trails are mainly used to record and retrieve surfing history information.

DESIGNING MEMEX FUNCTIONS USING SCPN

Simulating Memex Trail Recording in Web Browsing

To simulate Memex in Web browsing, we assume that a place in SCPN represents a Web site. Each time a Web site is opened, a color token including the following basic commands will be injected into the place p start that includes a resource token as shown in Figure 2: lock the resource token in p start , create a new place p 1 (this place will represent the newly opened Web site), create a new transition t 1 , create an arc from current place p start to the new transition t 1 , create an arc from the new transition t 1 to the new place p 1 , unlock the resource token in p start . Finally, the color token self-deletes, transition t 1 fires, the resource token moves to p 1 indicating that the Web site represented by this place is active now. While SCPN is recording the surfing trail, the corresponding Web site address will be recorded along with each place.

Main Trail and Side Trails

Almost all Web sites contain some related hyperlinks. A trail can bifurcate: when a hyperlink of one Web site is visited, a side-trail will be created to record it. As
shown in Figure 3, the main trail that represents the main surfing history is composed by places with m as the first subscript, the side-trail that represents the hyperlink of a Web site is composed by places with names having s as the first subscript.

If the hyperlink is opened in a new window or the user wants to record the hyperlink of a Web site as a new trail, a new starting place will be created as the first place in a new trail as shown in Figure 4. The arcs linking from p m1 to p m’1 are represented by dot lines meaning that these arcs do not allow a reverse token moving along them.

Backward and Forward Operations

Using SCPN to record a browser trail, it can simulate the backward and forward operations of Web browsing. A resource token in a place indicates that the Web site corresponding to this place is active, the arcs indicate the sequence of Web sites being visited. When a user issues a backward command, a color token corresponding to this command will be injected into the place p m3 that includes a resource token as shown in Figure 5a. Then the commands associated with this color token executes, the resource token in p m4 is locked and changed to a reverse one as shown in Figure 5b. In Figure 5c, the reverse token is unlocked and the color token self-deletes. Finally, transition t m3 fires, the reverse token moves from p m3 to p m2 and changes back to forward resource token as shown in Figure 5d, the information of the Web site related to place p m2 will be retrieved. At the same time, p m3 is recorded as an exit point so that a future forward move will allow p m3 to be revisited.

After checking the content of this Web site, if the user decides to go back to the previous Web site again, a forward command can be issued. A color token associated with the forward command will be injected into place p m2 that contains the resource token as shown in Figure 6a. Then the command executes to direct the resource token to fire. At this moment, we can see that one of the two transitions t m3 and t s21 can fire. In modeling Memex functions, SCPN is used to record the surfing history, the resource token is used to indicate the active Web site. There can be only one place that can contain the resource token at a time. In such a forward operation, because the exit point of a previous backward operation has been recorded, t m3 will fire and the resource token will move to p m3 as shown in Figure 6b, at the same time, the record of the previous exit point will be replaced by p m2 for future use.

SIMULATOR

Using Visual C++, a simulator has been built. This simulator can model Memex functions such as trail recording and retrieval. To make the simulation more realistic, we use the Microsoft Active X® controller in our program to display a Web site visited at the same time when the SCPN place corresponding to the Web site is created or a resource token is injected into the place. A user can click the buttons as shown in Figure 7 to simulate the corresponding function.

To make the simulator more powerful, a basic Petri Net design tool is provided. A Petri Net instance can be designed simply by clicking and dragging the icons from the toolbar to the white area. The Petri Net instance created can be saved as a .mex file for future use. Also a RUN button as shown in the menu in Figure 7 is provided to execute a Petri Net instance. When the RUN button is clicked, the Petri Net instance will be executed. If the instance is active, the token will move according to the firing direction. The Back, Forward and History buttons are used to simulate Memex functions in a Web Browser. The Save button is used to save the trail. If some trails have been built, Search function can help a user to find an item of interest in these trails. We give an example to show how this simulator works.

As shown in Figure 8, when a Web site is opened (assume this is a new trail to be built), an event signal will be sent to the system indicating a new Web site is opened. With this event, a place will be created to record it. And a resource token will be created in the place at the same time to indicate that the Web site corresponding to this place is active. In order to let the user arrange trails according to his need, the simulator provides trail recording options. Each time when a Web site is opened, a dialog box will be popped up to ask the user if the Web site needs to be recorded as shown in Figure 9. If the user chooses not to archive this Web site, the place being created to record this Web site will be deleted after the Web site is closed. If the user puts down an existing trail name, the Web site will be added and recorded as the last place in this existing trail. If the user puts down a new trail name , a dialog box will be popped up to let the user choose how to record this Web site as shown in Figure 10. For example, if a hyperlink is followed after three Web sites have been visited, the user chooses to record it as a side trail by clicking the Yes button (Figure 10). This Web site will then be recorded as a side trail as shown in Figure 11.

As shown in Figure 12, there are five places in the SCPN instance shown. From this we know that five Web sites have been visited. The active Web site is http://www.google.com associated with the fifth place. SCPN can show how many Web sites have been visited and which one is active now, but no detailed information of these Web sites is shown on the graph. If the user wants to see the details of the Web sites visited, the History button in the menu can accomplish this task.

Using SCPN to record trails, each place is associated with a Web site. It is easy to display history records. When the user issues a command ’ History ’, this can be done by clicking on the History button, a dialog box will be opened to show the detailed trail information as shown in Figure 12.

With the trail shown, we can select any item to revisit. For example, if we want to visit the IEEE Xplore Web site, just select it from the list and click the ok button. The corresponding Web site will be retrieved and the resource token will move to p m4 as shown in Figure 13.

In addition to trail recording and retrieval, the Memex simulator can also achieve the backward and forward operations similar to those functions in Web browsers. As shown in Figure 14, if the user wants to visit the previous Web site before the IEEE Xplore Web site, he only needs to click the Back button . The resource token will move to p m3 and at the same time the Web site associated with this place will be opened.

Following the above example, if the user wants to visit the next Web site again, he only needs to click the Forward icon, the resource token will move to p m4 and the corresponding Web site will be reopened at the same time.

Besides these Web-browser-like operations, the most important Memex function is that when some trails have been built, a user can search for it according to name/topic/keyword. As shown in Figure 15, when a user clicks the Search button, a dialog box will be popped up to show the existing trails. Then the user can select from these trails the one that he is interested in to retrieve or input it in the search Edit-box. For example, if the user wants to find some information about Memex, he/she only needs to select the first item from the dialog box or input Memex into the search Edit-box and click the ok button. The Memex trail details will then be displayed in a dialog box. Then the user proceeds to choose a Web site he wants to visit from this trail. Assume that the first one is selected, the Web site will be opened and at the same time the trail represented by SCPN is displayed as shown in Figure 16. The resource token in p m1 indicates that the Web site associated with this place is active.

CONCLUSION

In this paper, we have given an introduction to a Self-modifiable Color Petri Net model – SCPN. With the powerful reconfiguration function offered from this model, Memex functions can be achieved in Web browsing. Our approach offers an underlying model with which a systematic approach to constructing Memex-like applications can be adopted. A simulator with user-friendly interface has been built to show how this can be achieved. This simulator can also be used as a Petri Net design tool to help users to design and implement their own Self-modifiable Color Petri Net instances.

Interactive Multimedia Technologies for Distance Education in Developing Countries - INTRODUCTION, BACKGROUND, MAIN FOCUS, FUTURE TRENDS, CONCLUSION [next] [back] Interactive Digital Television - BACKGROUND, A DEFINITION OF INTERACTIVITY, Local Interactivity, One-Way Interactivity, Two-Way Interactivity

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