W3C

Compact HTML
for Small Information Appliances

W3C NOTE 09-Feb-1998

This version:

http://www.w3.org/TR/1998/NOTE-compactHTML-19980209

Latest version:

http://www.w3.org/TR/1998/NOTE-compactHTML-19980209

Author:

Tomihisa Kamada, ACCESS Co.,Ltd., tomy@access.co.jp

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Status of this Document

This document is a NOTE made available by the W3 Consortium for discussion only. This indicates no endorsement of its content, nor that the Consortium has had any editorial control in it preparation, nor that the Consortium has, is, or will be allocating any resources to the issues addressed by the NOTE.

This document is a submission to W3C. Please see <http://www.w3.org/Submission/> Acknowledged Submissions to W3C regarding its disposition.

Abstract

The Internet infrastructure has been developed all over the world, and nowadays there are a variety of devices equipped with the Internet-access function, from TV sets to wireless cellular phones. The HyperText Markup Language (HTML) is widely accepted and spread as the standard of the WWW(World Wide Web) document format. The "Compact HTML" proposed here defines a subset of HTML for small information appliances such as smart phones, smart communicators, mobile PDAs, and etc. Such a certain level of HTML is strongly required as a guideline from the manufacturers of small information devices, service providers, carriers, and software developers. Since "Compact HTML" is completely based on the HTML recommendations, we can use millions of HTML-based content resources, various software tools, and public materials (textbooks, magazines, and web information).

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Contents

1. Introduction
2. Requirements of Small Information Appliances
   1. Scope of the Products
   2. Requirements
   3. Wireless Network
3. Definition of Compact HTML
   1. Design Principles
   2. Features of Compact HTML
   3. Detail Definition
4. Examples and Benefits of Compact HTML
   1. Examples
   2. Benefits of Compact HTML
   3. Another Approach
5. Concluding Remarks

References
Acknowledgments
Appendix A. Compact HTML Tag List
Appendix B. Compact HTML DTD

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1. Introduction

The Compact HTML is a well-defined subset of HTML 2.0[1], HTML 3.2[2] and HTML 4.0[3] recommendations, which is designed for small information appliances. HTML defines flexible, portable, and practical document format for the documents on the Internet. One direction of HTML is to grow toward richer multimedia document format. A new recommendation HTML 4.0[3] includes new additional features. For example, CSS(Cascading Style Sheets) give a wider range of document styles. On the other hand, there must be another direction for small information appliances. Small information appliances have several hardware restrictions such as small memory, low power CPU, small or no secondary storage, small display, mono-color, single character font, and restricted input method (no keyboard and mouse). The browser for Compact HTML proposed in this document can be implemented in such a restricted environment. Once such a subset of HTML is defined, contents providers and information appliance manufacturers can rely on this common standard. We believe that Compact HTML definitely contributes to the rapid growth of small information appliance market.

2. Requirements of Small Information Appliances

2.1. Scope of the Products

First we describe the scope of target small information appliances. The categories of these devices are often referred to as smart phones, smart communicators, and mobile PDAs. There are some hardware restrictions for these devices. From the hardware point of view, we pick up main characteristics of the target devices.

• Small memory
  Typical case: 128-512Kbytes RAM
  and 512K-1Mbytes ROM
  
• Low power CPU
  Typical case: 1-10 MIPS class CPU for embedded systems
  
• Small display
  Typical case: 50x30 dots, 100x72 dots, and 150x100 dots
  
• Restricted colors
  Typical case: mono-color (black and white)
  
• Restricted character fonts
  Typical case: only single font
  
• Restricted input method
  Typical case: several control buttons and number buttons (0-9)

The picture shows an example of cellular phone which has the HTML browsing function. A wide variety of content services are potentially possible via wireless networks.

2.2. Requirements

To realize the WWW browsing function for such small devices, a suitable subset of HTML is necessary. The requirements are derived from the above hardware restrictions. Also these devices should be easy to use from the standpoint as consumer products. The browser software for a subset of HTML should run within the small memory: e.g., 150-200Kbytes for the working data and also 150-200Kbytes for the program code. The minimum requirement for the CPU power should be 1-2 MIPS, though it may depend on the CPU power required for network communication processing. Easy navigation is also one of the key features for consumer devices. It means that the users can navigate information with a minimum number of operations. A subset of HTML should satisfy this requirement.

2.3. Wireless Network

Compact HTML does not depend on the underlying network protocol. In the typical cases, the transport protocol for Compact HTML is assumed to be HTTP over TCP/IP. However, current wireless communication networking for cellular phones is low band and low speed. In this area, the transport protocol should be defined as light protocol for better performance on the physical packet layer. It also seems useful to compress HTML contents so that most of HTML data can be stored within one packet data.

3. Definition of Compact HTML

3.1 Design Principles

The Compact HTML is designed to meet the requirements of small information appliances described above. It is designed based on the following four principles.

The definition of Compact HTML is derived straightforwardly from the above principles.

3.2 Features of Compact HTML

The Compact HTML is a subset of HTML 2.0, HTML 3.2 and HTML 4.0. We describe the major features which are excluded from Compact HTML, as follows.

• JPEG image
• Table
• Image map
• Multiple character fonts and styles
• Background color and image
• Frame
• Style sheet

We define that Compact HTML includes GIF image support. It should be noted that this subset does not require two-dimensional cursor moving, that is, it can be operated by using only four buttons. We can also expect that well-designed pages for small display fit the screen space and the scrolling is not necessary. Actually the Compact HTML browser can display the pages like "deck of cards" by HDML[4].

Since the memory capacity is the most important issue in implementing the Compact HTML browser, we recommend the buffer limit for some functions.

• INPUT
  The maximum buffer size is 512 bytes.
• SELECT
  The maximum buffer size is 4096 bytes.

Though such a limitation belongs to the implementation issues, the common criteria is useful while developing devices.

One recommended implementation for the browser is to support the direct selection of anchors by using number buttons. For example, when five anchors are contained in an HTML page, the third anchor can be selected just by pressing the "3" button. (The HTML 4.0 specification includes a new attribute "accesskey" for the similar purpose of direct key assignment. )

3.3 Detail Definition

The complete list of tags supported by Compact HTML is described in Appendix A. The comparison with HTML 2.0, HTML 3.2 and HTML 4.0 is marked in the table. The document type definition (DTD) for Compact HTML is also described in Appendix B. This gives the intended interpretation of Compact HTML elements. The document type is defined as follows;

<!DOCTYPE HTML PUBLIC "-//W3C//DTD Compact HTML 1.0 Draft//EN">

4. Examples and Benefits of Compact HTML

4.1 Examples

Here we describe the examples of applications by using Compact HTML. The following examples show the compact browser for cellular phones. The screen is the space of 7 text lines and 16 characters wide. The top line is used for displaying the status information.

Practical implementations and experiments show that Compact HTML is enough useful for small screen of 5-10 text lines and 10-20 characters wide.

4.2 Benefits of Compact HTML

The Compact HTML, an HTML-based approach, guarantees that small information appliances can connect to the open WWW world. Compact HTML keeps the advantage of HTML features and solves the problems arising from the restrictions of small information appliances.

The Compact HTML specification can be referred to by the tools like HTML authoring systems. In addition, the client-specific web services for such small devices can be realized by using user agent attributes [5]. That is, the server can do the content filter for Compact HTML.

4.3 Another Approach

There may be another approach which is NOT based on HTML standards. The approach of a new language may be accepted in a certain closed service. For example, a language named HDML(Handheld Device Markup Language)[4] is proposed for the mobile handheld devices. The goal of HDML is very similar to the one of Compact HTML. It seems useful for a class of handheld devices. However, the disadvantage of special language approach can be said that everything such as contents, authoring tools, server software, client software, and textbooks have to be prepared. Especially thinking about a product line from high-end PDAs to low-end cellular phones, the consistent HTML-based approach would make sense.

5. Concluding Remarks

We proposed the Compact HTML for small information appliances. This contributes to the WWW community, especially for wireless and mobile small devices. Compact HTML can be referred as a recommended guideline for HTML services and for HTML browsing software in this area.

The Internet world is growing very fast. Several levels will be likely required for Compact HTML in the near future. It is important to evolve the functionality and extend the specification flexibly, according to the requirements from the growing market.

In the early 21st century, the world-wide standard for wireless digital phone networking protocols will be established. The band width of the network is expected to be wide enough for motion picture (video) communications. Compact HTML should include such advanced features in this next generation of wireless network.

References

Acknowledgments

We would like to thank to Professors Nobuo Saito and Tatsuya Hagino (KEIO University) and many W3C members for their supports and suggestions. We are also grateful to NTT DoCoMo for their supports to Compact HTML for wireless cellular phones.

Appendix A. Compact HTML Tag List

--Updated 1998年01月27日
--HTML(2.0:HTML2.0, 3.2:HTML3.2, 4.0:HTML4.0)
--CH:Compact HTML

Appendix B. Compact HTML DTD

<!-- Compact HTML Document Type Definition -->
<!--
 Date: Tuesday November 25th 1997
 Author: Tomihisa Kamada <tomy@access.co.jp>
-->
<!ENTITY % HTML.Version
 "-//W3C//DTD Compact HTML 1.0 Draft//EN"
 >
<!--================== Deprecated Features Switch =========================-->
<!ENTITY % HTML.Deprecated "INCLUDE">
<!--================== Imported Names =====================================-->
<!ENTITY % Content-Type "CDATA">
<!ENTITY % HTTP-Method "GET | POST">
<!ENTITY % URL "CDATA">
<!-- Parameter Entities -->
<!ENTITY % heading "H1|H2|H3|H4|H5|H6">
<!ENTITY % list "UL | OL | DIR | MENU">
<!ENTITY % preformatted "PRE">
<!--================ Character mnemonic entities ==========================-->
<!ENTITY % ISOlat1 PUBLIC
 "ISO 8879-1986//ENTITIES Added Latin 1//EN//HTML">
%ISOlat1;
<!--================ Entities for special symbols =========================-->
<!ENTITY amp CDATA "&" -- ampersand -->
<!ENTITY gt CDATA ">" -- greater than -->
<!ENTITY lt CDATA "<" -- less than -->
<!--=================== Text Markup =======================================-->
<!ENTITY % phrase "DFN">
<!ENTITY % special "A | IMG | BR ">
<!ENTITY % form "INPUT | SELECT | TEXTAREA">
<!ENTITY % text "#PCDATA | %phrase | %special | %form">
<!ELEMENT (%phrase) - - (%text)*>
<!ELEMENT BR - O EMPTY>
<!ATTLIST BR
 clear (left|all|right|none) none 
 >
<!--================== HTML content models ================================-->
<!ENTITY % block
 "P | %list | %preformatted | DL | DIV | CENTER |
 BLOCKQUOTE | FORM | HR ">
<!ENTITY % flow "(%text | %block)*">
<!--=================== Document Body =====================================-->
<!ENTITY % body.content "(%heading | %text | %block )*">
<!ELEMENT BODY O O %body.content>
<!ELEMENT DIV - - %body.content>
<!ATTLIST DIV
 align (left|center|right) #IMPLIED
 >
<!ELEMENT center - - %body.content>
<!--================== The Anchor Element =================================-->
<!ELEMENT A - - (%text)* -(A)>
<!ATTLIST A
 name CDATA #IMPLIED
 href %URL #IMPLIED
 >
<!--=================== Images ============================================-->
<!ENTITY % Length "CDATA">
<!ENTITY % Pixels "NUMBER">
<!ENTITY % IAlign "(top|middle|bottom|left|right)">
<!ELEMENT IMG - O EMPTY>
<!ATTLIST IMG
 src %URL #REQUIRED
 align %IAlign #IMPLIED
 width %Pixels #IMPLIED
 height %Pixels #IMPLIED
 hspace %Pixels #IMPLIED
 vspace %Pixels #IMPLIED
 alt CDATA #IMPLIED
 border %Pixels #IMPLIED
 >
<!--=================== Horizontal Rule ===================================-->
<!ELEMENT HR - O EMPTY>
<!ATTLIST HR
 align (left|right|center) #IMPLIED
 size %Pixels #IMPLIED
 width %Length #IMPLIED
 noshade (noshade) #IMPLIED
 >
<!--=================== Paragraphs=========================================-->
<!ELEMENT P - O (%text)*>
<!ATTLIST P
 align (left|center|right) #IMPLIED
 >
<!--=================== Headings ==========================================-->
<!ELEMENT ( %heading ) - - (%text;)*>
<!ATTLIST ( %heading )
 align (left|center|right) #IMPLIED
 >
<!--=================== Preformatted Text =================================-->
<!ENTITY % pre.exclusion "IMG">
<!ELEMENT PRE - - (%text)* -(%pre.exclusion)>
<!--=================== Block-like Quotes =================================-->
<!ELEMENT BLOCKQUOTE - - %body.content>
<!--=================== Lists =============================================-->
<!ELEMENT DL - - (DT|DD)+>
<!ELEMENT DT - O (%text)*>
<!ELEMENT DD - O %flow;>
<!ELEMENT (OL|UL) - - (LI)+>
<!ELEMENT (DIR|MENU) - - (LI)+ -(%block)>
<!ELEMENT LI - O %flow>
<!--================ Forms ===============================================-->
<!ELEMENT FORM - - %body.content -(FORM)>
<!ATTLIST FORM
 action %URL #IMPLIED
 method (%HTTP-Method) GET
 enctype %Content-Type; "application/x-www-form-urlencoded"
 >
<!ENTITY % InputType
 "(TEXT | PASSWORD | CHECKBOX | RADIO | HIDDEN 
 | IMAGE | SUBMIT | RESET )">
<!ELEMENT INPUT - O EMPTY>
<!ATTLIST INPUT
 type %InputType TEXT
 name CDATA #IMPLIED
 value CDATA #IMPLIED
 checked (checked) #IMPLIED
 size CDATA #IMPLIED
 maxlength NUMBER #IMPLIED
 src %URL #IMPLIED
 align %IAlign #IMPLIED
 >
<!ELEMENT SELECT - - (OPTION+)>
<!ATTLIST SELECT
 name CDATA #REQUIRED
 size NUMBER #IMPLIED
 multiple (multiple) #IMPLIED
 >
<!ELEMENT OPTION - O (#PCDATA)*>
<!ATTLIST OPTION
 selected (selected) #IMPLIED
 value CDATA #IMPLIED
 >
<!ELEMENT TEXTAREA - - (#PCDATA)*>
<!ATTLIST TEXTAREA
 name CDATA #REQUIRED
 rows NUMBER #REQUIRED
 cols NUMBER #REQUIRED
 >
<!--================ Document Head ========================================-->
<!ENTITY % head.content "TITLE & ISINDEX? & BASE?">
<!ELEMENT HEAD O O (%head.content)>
<!ELEMENT TITLE - - (#PCDATA)*>
<!ELEMENT BASE - O EMPTY>
<!ATTLIST BASE
 href %URL #REQUIRED
 >
<!ELEMENT META - O EMPTY>
<!ATTLIST META
 http-equiv NAME #IMPLIED
 >
<!--================ Document Structure ===================================-->
<!ENTITY % version.attr "VERSION CDATA #FIXED '%HTML.Version;'">
<!ENTITY % html.content "HEAD, BODY">
<!ELEMENT HTML O O (%html.content)>
<!ATTLIST HTML
 %version.attr;
 >
<!--================ End of DTD ===========================================-->