Helsinki University of Technology Telecommunications Software and Multimedia Laboratory T-111.590 Research Seminar on Digital Media Digital TV Services in Handheld Devices

12th May 2005

A Compound Document Format for Handheld Devices

Mikko Pohja 44305U

A Compound Document Format for Handheld Devices Mikko Pohja HUT, Telecommunications Software and Multimedia Laboratory [email protected]

Abstract Handheld devices have recently gained access to the Internet. The devices differ a lot from traditional desktop computers what comes to, for instance, browsing the Web. Several parties have defined specifications, which facilitates creating Web documents for handheld devices. In this paper, we have defined document profile, which combines many document formats targeted for handheld devices. The result is compound document profile, through which can be realized multimedia presentations in handhelds. The profile has two configurations, from which one can select depending on target device’s resources.

1 INTRODUCTION Nowadays, handheld devices have access to the Internet. However, there are some limitations in web browsing with restricted devices. For instance, screen size and processing power are notably smaller than in desktop computers. To browse current web pages with handheld devices can be difficult or even impossible. Several consortiums have addressed this problem by defining markup language specifications for handheld devices. World Wide Web Consortium (W3C) has published XHTML Basic and CSS Mobile Profile for handheld devices. W3C has also defined Scalable Vector Graphics (SVG) recommendation to present vector graphics in XML format. Through SVG the graphics can be presented properly even though screen sizes varies a lot between different devices. Recently, W3C started a Compound document formats working group1 . Its aim is to specify the behavior of some format combinations, namely XHTML, SVG, Synchronized Multimedia Integration Language (SMIL), and XForms combinations. Open Mobile Alliance (OMA) has introduced Wireless Application Protocol (WAP) 2.0 as a declarative environment for handheld devices. XHTML Mobile Profile (XHTMLMP) is part of Wireless Markup Language (WML) 2.0, which is the markup language of 1

http://www.w3.org/2004/CDF/

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WAP 2.0. Vodafone has made a proposal how to integrate XHTMLMP and SVG Tiny2 . In this paper we review what kind of requirements handheld devices set to a compound document format and what kind of format is suitable for handheld devices. Aspects, which were taken account when defining requirements, were representation of text, images, and 2D graphics, temporal layout of a document, and user interaction. We defined language profile, which consists of existing and proposed formats of markup languages. In addition, the profile is divided to two configurations depending on device’s resources. That is, most restricted devices are not able to handle all the graphical and temporal features of the defined profile. The rest of the paper is organized as follows. In next Section is discussed the markup languages used in this paper. Section 3 defines the requirements of the language profile and Section 4 introduces the implementation of the profile. Future work is defined in Section 5. Finally, Section 6 gives the conclusions of the work.

2 BACKGROUND Hypertext Markup Language (HTML) is used to create structured hypertext documents on the World Wide Web (WWW). HTML is based on Standard Generalized Markup Language (SGML). The Extensible HyperText Markup Language (XHTML) is a family of document types and modules that reproduce HTML, reformulated in eXtensible Markup Language (XML). XHTML is the successor of HTML. Several versions of XHTML have been developed. For handheld devices, there are XHTML Basic and XHTMLMP profiles. XHTML Basic includes the minimal set of XHTML modules defined in Modularization of XHTML (Altheim, 2001). XHTMLMP is a superset of XHTML Basic. In addition to XHTML Basic elements, XHTMLMP contains elements relating to forms, presentation and style element and attribute. Also, XHTML 2.0 (Axelsson, 2004), which is under development at W3C, is suitable for handheld devices. XHTML 2.0 is successor of the HTML languages, but it is not backward compatible with them. The origins and relationships between markup languages are depicted in Figure 1. Cascading Style Sheets (CSS) is a method for adding style to Web documents. CSS has also various levels and profiles. CSS Mobile Profile is for handheld devices. OMA has defined a WAP CSS profile, which is superset of CSS Mobile Profile. WAP CSS has the same properties as W3C’s CSS Mobile Profile and in addition few WAP specific properties (WAP Forum, 2002). SVG suits well to present 2D graphics on the WWW. The advantage of vector graphics is that it does not lose its accuracy when zooming. That is, graphics can be adjusted to all screen sizes. Integration of SVG to XHTML is vital to enable content usage in all devices. Currently, there are several SVG specifications defined by W3C. For mobile devices, there are two profiles, namely SVG Tiny and SVG Basic. Tiny is 2

XHTMLMP+SVGT, http://lab.vodafone.com/public/XHTMLMP-SVGT-Recommendations.html

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(Forum Nokia, 2003) Figure 1: Relationship between markup languages. for restricted mobile devices whereas Basic is targeted for higher level mobile devices. (Capin, 2003)

3 REQUIREMENTS The definitions of the requirements for the language profile are based on the ones used in Honkala et al. , 2004. The paper defines language profile for multimedia XML language. The profile should cover following aspects: spatial and temporal layout, support for media objects, and support for user interaction (i.e., links, user input, and submission). The requirements are described in Table 1. Defining spatial layout is vital in Web documents. There are two options to do it. One is XHTML and other is SMIL. SMIL provides only absolute position for laying out, whereas XHTML provides also flow layout. For hanheld devices, there are several XHTML profile options to select (e.g., XHTMLMP, XHTML Basic, or XHTML 2.0). In addition to layout, also text and images can be handled by both SMIL and XHTML. 2D graphics can be represented as any image in a SMIL or XHTML document. In addition, it can be represented through SVG. Temporal layout can be defined either by SMIL (Ayars, 2001) or Timesheets (ten Kate et al. , 2000, Jalava et al. , 2005). W3C has recently published a working draft of use cases and requirements for compound documents by reference (Appelquist et al. , 2005). The document defines requirements for a profile, which comprises XHTML, CSS and SVG. The profile sup3

Table 1: General requirements of the compound document format. Requirement Description Spatial layout Text Images 2D graphics Temporal layout User interaction Links User input Submission

Defines positions of media elements in a presentation. Handling of a text flow in a presentation. Handling of images in a presentation. Method to handle and display 2D graphics in a presentation. Synchronization of media elements of the presentation. Hyperlinks of a presentation. Method to retrieve user input. User input must be submitted to server.

ports presentation of rich multimedia content. Some of the requirements are also used in this paper for requirements of compound documents in handheld devices. The requirements are discussed in next Section.

4 IMPLEMENTATION In this section, we discuss the proposed language profile. First, we define with what technologies the requirements set above can be fulfilled. Second, we create two configurations from the profile to adjust it for different handheld devices.

4.1 Technologies In the proposed format, we chose XHTML and CSS to define the spatial layout instead of SMIL. XHTML provides more options to define the layout. In XHTML, elements can be laid out absolutely, relatively, or with the flow. Also, XHTML is particularly meant for textual layout, whereas SMIL is rather for positioning and synchronizing media objects. Laying out the images can be realized easily with both technologies. From several XHTML versions, we chose XHTML 2.0. XHTML 2.0 is a novel solution, which provides generally useful set of elements, which can also be handled by handheld device. XHTML 2.0 corrects errors and deficiencies identified in earlier versions of the HTML. For instance, in XHTML 2.0, the structure of document can be defined more strictly. A document can be divided to sections and subsections.

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Table 2: Technology resolutions for the compound document format. Requirement Description Spatial layout Text Images 2D graphics Temporal layout User interaction Links User input Submission

XHTML 2.0 + CSS XHTML 2.0 XHTML 2.0 SVG Timesheets XHTML 2.0 XForms XForms

The headers are decided automatically according to embedding levels. Also, many elements and attributes have more general usage, which makes the language more versatile. Finally, it uses XForms as a form technology, which offers a lot improvements compared to current HTML forms. Temporal layout can be realized either by SMIL (Ayars, 2001) or by Timesheets (ten Kate et al. , 2000, Jalava et al. , 2005). SMIL has some limitations (ten Kate et al. , 2000, van Ossenbruggen et al. , 2003) to be used as a common multimedia declaration language for all XML documents. Especially, when a document consists of several XML languages. In addition, when using SMIL the layout is defined by SMIL, too. Timesheets works the other way around. It is integrated into a host language’s layout system, which makes it possible to control single elements inside a document. In short, Timesheets assigns temporal relations between elements and sets styles for elements in temporal manner. Timesheets was selected to describe the temporal layout since it integrates better with compound documents. SVG was chosen to represent 2D graphics. SVG’s advantage is that it supports portability. Single SVG graphic can be used in devices with very different characteristics (e.g., screen size). There are two SVG version options for handheld devices. The selection between SVGT and SVG Basic depends on configuration. The user interaction is realized by XHTML 2.0. Any XHTML 2.0 element can be a hyperlink through href attribute. XHTML 2.0 contains XForms module, through which validated entries and server submission can be realized. The technology resolutions for the requirements are summarized in Table 2. To combine all the technologies together, we have defined some technology requirements for the format. W3C’s working draft of use cases and requirements for compound documents by reference (Appelquist et al. , 2005) was instrumental in defining the requirements. The requirements are discussed in Table 3. XHTML 2.0 is used as host language and it embeds both SVG and XForms elements. SVG is compounded by reference, but XForms by inclusion as usual in XHTML 2.0. User must be able to 5

Table 3: Technology requirements of the compound document format. Requirement Description Compound SVGT by reference. Compound XForms by inclusion.

XHTML 2.0 is used as a host language. Support for user interaction. Must support grid, flow, overlapping layouts. Must define transparency support for SVG backgrounds

Use XHTML object element to embed SVGT documents. XForms elements are mixed with XHTML at element level as defined in XHTML 2.0 specification. SVGT and XForms are combined with XHTML 2.0. Event and focus management between components should be supported. Elements may be positioned absolutely or with the flow. In addition, they may overlap each other. Support for static SVG background images.

interact with all the components of a document. That is, there has to be way to move focus between components, as well as events must flow from a component to another. Specific definitions of event and focus management are left as future work. Laying out is critical part of combining languages. In the proposed format, the elements can positioned either absolutely or with the flow of elements. In addition, they may overlap each other. It must be possible to layout and render elements from different languages on top of each other. Finally, SVGT graphics must be able to use as background images in a presentation.

4.2 Configurations Handheld devices have different characteristics. In this paper, we defined two configurations of the language for different devices. One is for mobile phones with restricted resources and other is for more powerful devices like PDAs. In compact configuration we have to go short of certain features to make it possible to use the profile in restricted devices. The comparison of selected technologies is discussed in Table 4. The compromises were done in the areas of 2D graphics, temporal layout, and form technology. For restricted configuration we chose SVG Tiny profile, while full configuration includes SVG Basic profile. Both profiles are meant for handheld devices as discussed in Section 2. Possibility to define temporal layout was left out in restricted configuration. Finally, restricted configuration uses XForms Basic (Dubinko & Raman, 2003) as form technology, whereas full configuration uses XForms Full. The differences of the profiles are the following features. XForms Basic Profile processors 6

Table 4: Comparison of the two configurations. Requirement Restricted Full Spatial layout Text Images 2D graphics Temporal layout User interaction Links User input Submission

XHTML 2.0 + CSS XHTML 2.0 XHTML 2.0 SVG Tiny None

XHTML 2.0 + CSS XHTML 2.0 XHTML 2.0 SVG Basic Timesheets

XHTML 2.0 XForms Basic XForms Basic

XHTML 2.0 XForms XForms

may support only XML Events Basic, XForms Basic Profile processors may implement a subset of an XML Schema processor, and they may treat some XML Schema datatypes as string.

5 FUTURE WORK A major detail, which we left as future work, is focus management. It is common problem for all compound document formats. The problem arises if there is not a pointing device in use. User must use, for instance, arrow keys instead. The navigating order of the focus points of a document, the rules how to jump from part of a document to another, and handling of dynamic cases have to be defined. Another future work is a reference implementation. By implementating an user agent, which supports both of the configurations defined in this paper, we could verify our design of compound document format for handhelds.

6 CONCLUSIONS Handheld devices can browse the Web nowadays. However, the Web documents are not often suitable for handhelds. We have defined general requirements for a handheld device language formats. According to the requirements, we defined a compound document format, which utilize several existing and proposed markup languages, to be to used as a markup for restricted devices. Since handheld devices have various resources, we defined two configurations, which differs by their graphical and multimedia features. The limited configuration is meant for small mobile phones, whereas full configuration is meant for PDAs and equivalent devices. Focus management should be still defined for the format. This is a common problem for all compound document formats and it should be solved generally. Also, we 7

would need an user agent, which supports the proposed format. With the user agent, we could verify our results.

REFERENCES Altheim Murray. 2001 (April). Modularization of XHTML. W3C Recommendation. W3C. Available at http://www.w3.org/TR/xhtml-modularization/. Appelquist Daniel, Mehrvarz Timur & Quint Antoine. 2005 (April). Compound Document by Reference Use Cases and Requirements Version 1.0. Working Draft. W3C. Available at http://www.w3.org/TR/2005/WD-CDRReqs-20050404/. Axelsson Jonny. 2004 (July). XHTML 2.0. Working Draft. W3C. Available at http://www.w3.org/TR/xhtml2/. Ayars Jeff. 2001 (August). Synchronized Multimedia Integration Language (SMIL 2.0). W3C Recommendation. W3C. Available at http://www.w3.org/TR/smil20/. Capin Tolga. 2003 (January). Mobile SVG Profiles: SVG Tiny and SVG Basic. W3C Recommendation. W3C. Available at http://www.w3.org/TR/SVGMobile/. Dubinko Micah & Raman T.V. 2003 (October). XForms 1.0 Basic Profile. Candidate Recommendation. W3C. Forum Nokia. 2003 (April). WML to XHMTL Migration. Tech. rept. 2.1. Nokia. Honkala Mikko, Cesar Pablo & Vuorimaa Petri. 2004 (December). A Device Independent XML User Agent for Multimedia Terminals. Pages 116–123 of: IEEE Sixth International Symposium on Multimedia Software Engineering. Jalava Teppo, Honkala Mikko, Pohja Mikko & Vuorimaa Petri. 2005 (April). Timesheets: XML Timing Language. Member Submission. W3C. Available at http://www.w3.org/Submission/xml-timing/. ten Kate Warner, Deunhover Patrick & Clout Ramon. 2000 (May). Timesheets - Integrating Timing in XML. In: WWW9 Workshop: Multimedia on Web. van Ossenbruggen Jacco, Hardman Lynda, Geurts Joost & Rutledge Lloyd. 2003 (May). Towards a Multimedia Formatting Vocabulary. Pages 384–393 of: Proceedings of the twelfth international conference on World Wide Web. WAP Forum. 2002 (January). Wireless Application Protocol WAP 2.0 Technical White Paper. White Paper. WAP Forum.

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