Creating, updating, and aggregating Web contents from different Web users and sites form the heart idea of Web 2.0. However, Web users originate from di erent communities, and follow their own semantics (referred to as local contexts in this paper) to represent and interpret Web contents. Therefore, several discrepancies could rise up between the semantics of Web authors and readers. In this paper, we present several Web 2.0 use cases, and illustrate the possible challenges and trends to handle the local contexts of Web users in these use cases.
The emerging results of community collaboration and contents mashups could not be achieved by individual users and individual Web sites, respectively. Each user gains more from the systems than he puts into it. Also, one Web site can not satisfy all the users' needs. Contents from di erent sites are to be aggregated and mixed together to satisfy complex users' requests. 1.1
The Web gathers billions of Web users from all over the world. These users
originate from di erent communities, and follow their local contexts for interacting
with Web contents. By local context, we means a set of common knowledge such
as a common language and common cultural conventions such as measure units,
keyboard con gurations, character sets, notational standards of writing times,
dates, numbers, currency [
Since di erent communities usually have di erent local contexts, a same concept (a Web concept) could be represented di erently by di erent Web authors. Also, the same Web content (the representation of a Web concept) could be interpreted in di erent ways by di erent Web readers. Hence, several discrepancies could be arisen between the semantics of Web authors and readers. For example, assume a French reader who wants to interpret a price Web content which is authored by a British author. In this context, the price is represented in British Pound and follows the British currency format (e.g., 1,234.50). As the French currency is Euro and di erent format is used (e.g., 1 234,50), the price must be converted from British Pound to French Euro by the reader. Note that the situation can be even worse if the reader wants to interpret a date content. The reader could misinterpret the date content (e.g., 07/08/2008) as the 7th of August 2008 (following the French format) instead of the 8th of July 2008 (following the British format). Similar situations may occur with other pieces of Web contents that are related to users' local contexts. 1.2
The emergence of the Web 2.0 raises new challenges. Web contents in a single page can be authored (created and updated) by several authors who have di erent local contexts. Moreover, contents authored from several authors on several Web sites could be dynamically aggregated, mixed, and displayed together in a single Web page. This paper presents several possible Web 2.0 use cases and explores some possible challenges and trends for handling users' local contexts in these use cases.
This paper is organized as follows. Section 2 presents several Web 2.0 use cases. Section 3 introduces a set of concepts that could be represented and interpreted according to users' local contexts and the challenges of handling them in the Web 2.0 use cases. Section 4 introduces semantic annotation as a possible solution. Finally, Section 5 concludes the paper. 2
In this section, we describe several possible use cases that users could perform when they use Web 2.0 systems. By no means we aim at covering all Web 2.0 use cases, but we attempt to classify the aforementioned Web 2.0 features (i.e., community collaboration and contents mashups) into three use cases: Web contents creation, Web contents update, and Web contents aggregation. 2.1
Several Web 2.0 systems enable Web authors to create Web contents, without giving the opportunities to update the published contents or parts of them. We focus on the Web contents creation in this use case. To illustrate this, let us consider the following Web 2.0 services: { Weblog (also called blog). Web 2.0 systems such as WordPress6 allow a single author to create Web contents (e.g., scienti c articles,privacy issues, etc.) called post, whereas other secondary users can add comments to contents created by the original author as new html nodes. { Bulletins Section. Web 2.0 social systems such as Facebook 7 and M ySpace provide a service to a group of users called \bulletin board". Bulletin board allows a user to add a piece of Web content (e.g., text message), whereas other users on the group list can see this content. Bulletins can be useful to contact an entire friends list without resorting to messaging users individually. { Group Section. Social systems also provide a service called \group section".
One or more users can create a common page (i.e., group section). The group creator(s) can invite any one to join, deny user's join request, delete or update users' contents, etc. Joined users, in addition to the group creator(s), usually can browse and create contents on the group section. 2.2
Several Web 2.0 systems enable Web authors to update Web contents after publishing. In this use case, a Web author could update the Web contents that she/he creates (referred to as a personal contents update) or the Web contents that other Web authors create (referred to as a community contents update). The following Web 2.0 services illustrate this use case: { Personal contents update. Web 2.0 commerce systems such as eBay8 allow a Web user to update the contents about the items she/he wants to sell. A user can update the contents concerning these items like the price, the photos, the selling location, etc. Other users can not change these pieces of contents. In addition, social systems allow a user to update his own pro le such as login name and password, preferred language, interests, etc.
{ Community contents update. Wiki systems such as Wekipedia allow one or more users (usually authorized users) to create Web contents as a set of interlinked Web pages and update these contents using creating and editing services. For example, a Web user can de ne the term local context or update the existing de nition authored from other author(s). In addition, collaborative editing systems such as Google Docs allow a group of users (might be from di erent locations) to collaboratively create and update documents (e.g., word document) online. Finally, the group creator(s) of the group section presented above can update the contents created by joined users. 2.3
Several Web 2.0 systems and technologies provide Web contents aggregation
and mixing services. In this sense, the aggregation and mixing services could be
performed on client-side (referred to as a client-side aggregation) or on a speci c
server-side application (referred to as a server-side aggregation). The following
Web 2.0 services illustrate this use case:
{ Client-side aggregation. RSS feed reader (aggregator) is the most known
technology that allows client-side applications (e.g., Web browser) to nd
out and collect Web contents from RSS-enabled Web sites9. In addition,
Piggy bank [
Finally, several E-commerce systems compose Web services together (e.g., airplane ticket reservation, car rental reservation, and hotel reservation) from di erent service providers (i.e., Web sites) to satisfy a complex user request.
In this sense, we can assume these systems as server-side aggregators.
3
As we mentioned, several discrepancies could be arisen between the semantics of Web authors and readers, since they could have di erent local contexts. In this section, we initially presents a set of concepts that could be represented and interpreted according to users' local contexts. Then, we discuss the challenges of handling the local contexts of these concepts in the above Web 2.0 use cases. 3.1
Based on local context, we aim at classifying Web concepts into
context12sensitive and non-context-sensitive concepts. Context-sensitive concepts refer to
the concepts which could be represented in di erent ways by di erent authors.
The following list identi es a set of context-sensitive concepts. By no means we
claim that this list covers all context-sensitive concepts, but we try to address
the main concerns that are rose up in the aforementioned use cases [
We can conclude that the local context represents a part of the semantic for the above Web concepts. Also, the semantic discrepancies that could arise do not relate to these concepts themselves, but rather to the local contexts of Web authors and readers that are implicity used when they represent and interpret these concepts.
In order to address this issue, several approaches have been proposed to
adapt Web contents to be suitable to readers' local contexts [
However, the use cases presented above illustrate that these assumptions are not valid anymore. Web contents are shared (created, updated, and aggregated) from di erent sources (i.e., Web users and Web sites). Hence, they are represented according to di erent local contexts and have heterogenous semantics. Therefore, the following challenging issues should be tackled: 1. Semantic identi cation. What is the information that required to identify the semantics of Web contents and the local contexts of Web users? 2. Semantic information management. How can the contents' semantics and the users' local contexts information be managed in terms of acquiring, representing, and storing this information? Also, what is the local context that used for representing each piece of Web content?
As mentioned before, Web contents could be created, updated, and aggregated from di erent sources. In this sense, di erent Web contents from di erent sources could refer to the same context-sensitive concept. For example, di erent authors could use cost, price, and amount contents to refer to the price concept. In addition, the value of the price concept could be represented in di erent ways, according to the authors' contexts.
Moreover, Web contents can be stored, aggregated and hosted on the serverside and can be aggregated and presented on the client-side. Server-side and client-side applications can not interpret Web contents if they are represented only using XHTML. Hence, a server-side application can not be aware if Web contents such as cost, price, and amount refer to the price concept or not, and it can not know which local context was used for representing them.
In this sense, several questions could be raised here. Firstly, what is the information that required to identify the semantics of Web contents, so that server-side and/or client-side applications can interpret that Web contents from di erent sources refer to one context-sensitive concept? Secondly, what is the (minimum) information required to identify the users' (authors and readers) local contexts, so that server-side and/or client-side applications can adapt Web contents from authors' contexts to readers' contexts. One could argue that the local context depends on users' countries, which can be obtained from the IP address contained in the HTTP header. However, this assumption is not valid as one country can have several communities (e.g., Belgium). Another question: how can we identify the local contexts of cross-sites aggregated contents?
In addition to the aforementioned issues, the information required to identify the semantics of Web contents and the local contexts of Web users needs to be acquired, represented, and stored.
In this sense, several questions have to been tackled. Firstly, how can the required information be acquired from di erent sources (i.e., users and sites). Assume the Web contents creation and update use cases. Does the required information be acquired directly from the authors or be acquired (predicted) from the server-side applications? Also, when the required information be acquired? (i.e., before contents creation or update, during contents creation or update). Assume the Web contents aggregation use case. How can this information be acquired from di erent sites.
Secondly, how should the required information be represented and where it should be stored (i.e., on the server-side or on the client-side), so that the local contexts of context-sensitive concepts can be handled in the above use cases. For example, the required information should be accessible from the client-side applications in order to handle the client-side aggregated contents. Also, it should be accessible from the server-side applications in order to handle the server-side aggregated contents.
Finally, how to specify the local context that used for representing each piece of Web content? Assume the community update use case where one Web author can update the contents created by other authors (e.g., Wiki contents). The question here: are the updated contents related to the context of the original author or the context(s) of the author(s) who update these contents? Moreover, assume, in contents aggregation use case, the case where the authors' local contexts for parts of the aggregated contents are not speci ed. How can this case be handled? 4
One possible solution to handle the aforementioned challenges is to directly rely
on the authors for annotating Web contents with semantic metadata, so that
the former become machine interpretable [
In addition, semantic metadata are accessible from server-side and client-side applications, as they are combined with Web contents. In the content aggregation use case, Server-side and/or client-side applications aggregate Web contents together with the corresponding semantic metadata. Finally, the Web authors, in contents update use case, should update Web contents and also the corresponding semantic metadata.
In this eld, there are two alternative approaches. The rst approach aims
at standardizing the representation of Web contents and their semantics for
all sources. For example, representing the Date/Time concepts according to the
ISO 8601 speci cation17. The second approach aims at allowing authors to
represent Web contents in di erent ways, but explicitly annotate them with semantic
metadata (i.e., contents' semantics and authors' local contexts). Microformats
technology18 follows the rst approach and RDFa19 technology follows the
second one [
Microformats propose a set of standards, or speci cations, and reuse XHTML attributes such as id and class to embed those speci cations into XHTML documents. For example, the hCard speci cation identi es vocabularies based on the vCard20 speci cation that provide semantic information about people and organization. Microformats speci cations standardize the representation of Web contents and their semantics at di erent three levels as follows: { Schema level. Identifying a speci c schema for each Microformats speci cation in terms of concepts and sub-concepts (called classes and subclasses) that can appear and their cardinalities (e.g., required, optional, etc.), the ordering of schema classes, etc. For example, hCard should have vcard class, f n and n subclasses at minimum. { Concept level. Identifying a speci c semantic vocabulary (Semantic label) for every class and subclass in each Microformats speci cation. Therefore, standardizing contents' semantics. { Representation level. Identifying a speci c representation for each class's and subclass's values. The authors should follow these representations as much as possible, so that Microformats parsers can interpret these representations. Therefore, standardizing authors' local contexts.
Server-side and/or client-side applications can interpret Web contents
annotated with Microformats (i.e., exchange, aggregate, adapt, etc.) without signi
cant loss of meanings. However, Microformats are not extensible and do not
fulll all authors' use cases. In our previous work, we conclude that Microformats
remain rather limited as they propose a nite set of speci cations [
RDFa provides a more abstract solution that aims at expressing RDF statements in XHTML documents. More precisely, RDFa provides a collection of XHTML attributes (reuses existing attributes such as content and rel and introduces new ones such as about and property) to embed RDF statements in XHTML, whereas it provides processing rules for extracting RDF statements from XHTML.
Web authors can reuse existing RDF-based semantic metadata (e.g., Dublin
Core and FOAF metadata) and create their own semantic metadata. Therefore,
RDFa is fully extensible. However, since Web contents and semantic metadata
from di erent sources are represented in di erent ways; the interpretation of
these contents (i.e., exchange, aggregation, adaptation, etc.) require a prior
semantic reconciliation between server-side and client-side applications [
In [
The main strength of the Web lies in its capacity to interconnect billions of
users from all around the world. However, this gathering of communities can
lead to the misunderstanding of Web contents as each community of users uses
its own context for interacting with Web contents. In this paper, we identi ed
new challenges in improving the context interpretation of Web contents in some
typical Web 2.0 use cases. We also explained how existing technologies such as
RDFa and Microformats can help people to better understand each other on the
Web. Based on [