2004/id/draft-seidman-html-clientsideimagemap-01.txt


INTERNET-DRAFT                                          James L. Seidman
<draft-ietf-html-clientsideimagemap-01.txt>             Spyglass, Inc.
Expires SIX MONTHS FROM--->                             August 8, 1995

      A Proposed Extension to HTML : Client-Side Image Maps

Status of this Memo

   This document is an Internet-Draft. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups. Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet-
   Drafts as reference material or to cite them other than as
   "work in progress."

   To learn the current status of any Internet-Draft, please check
   the "1id-abstracts.txt" listing contained in the Internet-
   Drafts Shadow Directories on ds.internic.net (US East Coast),
   nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or
   munnari.oz.au (Pacific Rim).

   Distribution of this document is unlimited.  Please send
   comments to the HTML working group (HTML-WG) of the
   Internet Engineering Task Force (IETF) at <html-wg@oclc.org>.
   Discussions of the group are archived at
   URL: http://www.acl.lanl.gov/HTML_WG/archives.html.

Abstract

   The markup language known as "HTML/2.0" provides for image maps.
   Image maps are document elements which allow clicking on different
   areas of an image to reference different network resources, as
   specified by Uniform Resource Locators (URIs).  The image map
   capability in HTML/2.0 is limited in several ways, such as the
   restriction that it only works with documents served via the "HTTP"
   protocol, and the lack of a viable fallback for users of text-only
   browsers.  This document specifies an extension to the HTML
   language, referred to as "Client-Side Image Maps," which resolves
   these limitations.
   
Table of Contents

   1.  Introduction
       1.1  Purpose
       1.2  Overall Operation
   2.  Client-Side Image Map Extension
       2.1  Syntax
       2.2  Required Changes to HTML/2.0 DTD
       2.3  Backwards Compatibility
       2.4  Examples
   3.  References
   4.  Author's Address


1. Introduction

1.1  Purpose

   Image maps are an important feature of the point-and-click
   interface which makes the World Wide Web so popular. The most
   common use of image maps is to allow users to access different
   documents by clicking on different areas in an image.

   There are several limitations of the current image map
   implementation as it applies to this use. First, it only works
   over the HTTP protocol, making it unusable for reading local files
   or files accessed via alternate protocols. Second, a server
   transaction is required merely to determine where the link is
   directed. This can degrade performance noticeably when accessing
   distant sites. Third, unlike for normal links, there is no way for
   a browser to provide visual feedback to the user showing where a
   portion of an image map leads before the user actually clicks on
   it. Lastly, the method for specifying the active regions of image
   maps is server-dependent, compromising portability of documents.
   This extension to support client-side image maps addresses these
   issues.

   It is proposed that this extension be included in a future revision
   of the HTML specification.

1.2  Overall Operation

   Client-side image maps work by placing a complete representation of
   the active areas of an image, including their shape, size, and
   destination (URI), into an SGML-compliant textual form.  This
   markup may also optionally include a textual description for
   each area for display on non-textual browsers.  This
   representation, or "map," is given a name to identify it.

   When an image is included in an HTML document, it may include an
   attribute specifying a map to use.  The map may contained in the
   same file which references the image, but this it not required.
   If the map is in a different file, a URI to that file must be
   provided.

   The browser will parse the map and remember the contents.  When the
   user clicks on the map, the browser will match up the location with
   the specified destination for that location and access that URI.
   In the case of a non-graphical browser, the browser could display
   the textual descriptions for each area instead of the image.
   Clicking on a given textual description would then go to the
   associated destination. 


2. Client-Side Image Map Extension

2.1 Syntax
   
   Adding a USEMAP attribute to an IMG element indicates that it is a
   client-side image map.  The USEMAP attribute can be used with the
   ISMAP attribute to indicate that the the image can be processed as
   either a client-side or server-side image map.  The argument to
   USEMAP specifies which map to use with the image, by specifying the
   URI for the file containing the map, followed by a '#', followed by
   the name of the map.  If the argument to USEMAP starts with a '#',
   the map is assumed to be in the same document as the IMG tag.  The
   presence of a USEMAP attribute overrides the effect of an enclosing
   anchor (A) element.
   
   The different regions of the image are described using a MAP
   element.  The map describes each region in the image and indicates
   where it links to. The basic format for the MAP element is as
   follows:

   <MAP NAME="name">
   <AREA [SHAPE="shape"] COORDS="x,y,..." [HREF="reference"]
         [NOHREF] [ALT="alt"]>
   </MAP>

   The NAME attribute specifies the name of the map so that it can be
   referenced by an IMG element.  Each AREA element contained inside
   the map element specifies a single clickable area of the image.
   The SHAPE attribute gives the shape of this area.  Possible shapes
   are "RECT", "CIRCLE", and "POLYGON", which specify rectangular,
   circular, and polygonal regions respectively.  If the SHAPE tag is
   omitted, SHAPE="RECT" is assumed.
   
   The COORDS tag describes the position of an area, using image
   pixels as the units with the origin at the upper-left corner of the
   image.  For a rectangle, the coordinates are given as
   "left,top,right,bottom".  The rectangular region defined includes
   the lower-right corner specified, i.e. to specify the entire area
   of a 100x100 image, the coordinates would be "0,0,99,99".
   
   For a circular region, the coordinates are given as
   "center_x,center_y,radius", specifying the center and radius of the
   circle.  All points up to and including those at a distance of
   "radius" points from the center are included.  For example, the
   coordinates "4,4,2" would specify a circle which included the
   coordinates (2,4) (6,4) (4,2) and (4,6).

   For a polygonal region, the coordinates specify successive
   vertices of the region in the format "x1,y1,x2,y2,...,xn,yn".
   If the first and last coordinates are not the same then a segment
   is inferred to close the polygon.  The region includes the
   boundary lines of the polygon.  For example, "20,20,30,40,10,40"
   would specify a triangle with vertices at (20,20) (30,40) and
   (10,40).  No explicit limit is placed on the number of vertices,
   but a practical limit is imposed by the fact that HTML limits
   an attribute value to 1024 characters.

   The NOHREF attribute indicates that clicks in this region should
   perform no action.  An HREF attribute specifies where a click in
   that area should lead.  A relative anchor specification will be
   expanded using the URI of the map description as a base, rather
   than using the URI of the document from which the map description
   is referenced. If a BASE tag is present in the document containing
   the map description, that URI will be used as the base.

   An arbitrary number of AREA tags may be specified.  If two areas
   intersect, the one which appears first in the map definition takes 
   precedence in the overlapping region.  Multiple areas may share the
   same destination to create composite shapes.  Any portion of an
   image which is not described by an AREA tag defaults to having no
   action.

   The ALT attribute specifies optional text which describes a given
   area.  A text-only browser can display the textual contents for
   each area as a substitute for the image.

2.2  Required Changes to HTML/2.0 DTD

   The required changes to the HTML/2.0 DTD to support this syntax
   would be as follows:

      Change the IMG element definition to be:
        <!ELEMENT IMG    - O EMPTY>
        <!ATTLIST IMG
                SRC %URI; #REQUIRED
                ALT CDATA #IMPLIED
                ALIGN (top|middle|bottom) #IMPLIED
                ISMAP (ISMAP) #IMPLIED
                USEMAP %URI; #IMPLIED
                %SDAPREF; "<Fig><?SDATrans Img: #AttList>#AttVal(Alt)</Fig>"
        >
           
      Add the following new definitions:
        <!ELEMENT MAP    - - +(AREA)>
        <!ATTLIST MAP
                NAME %linkName; #REQUIRED
        >

        <!ELEMENT AREA   - O EMPTY>
        <!ATTLIST AREA
                SHAPE (RECT|CIRCLE|POLYGON) RECT #IMPLIED
                COORDS CDATA #REQUIRED
                HREF %URI; #IMPLIED
                NOHREF (NOHREF) #IMPLIED
                ALT CDATA #IMPLIED
        >


2.3  Backwards Compatibility

   This extension is specifically designed to provide a variety of
   fallback options for browsers which do not support it.  These
   options are based on the assumption that browsers will ignore any
   attributes or elements which are not present in the HTML/2.0 DTD.

   An document can be written so that a client-side image map can have
   three different fallback behaviors.  First, the document can use
   the server-side image map capability, by specifying the ISMAP
   attribute as well as USEMAP.  In situations where this is possible,
   the image map will work whether or not the browser supports the
   client-side extension.

   Second, clicking on the image can direct the user to a single URI,
   regardless of where on the image he clicks.  This is accomplished
   by placing the image inside an anchor (A) element.  The fallback
   destination could provide the user with an error or a textual list
   of destinations.
  
   Lastly, the image can appear to not be a link at all (i.e. missing
   whatever visual cues a browser provides to indicate a hyperlink).
   This will be the result if the image element neither contains an
   ISMAP attribute nor is inside an anchor.

2.4  Examples

   The following three examples show markup demonstrating the three
   fallback mechanisms described in section 2.3:

      This image map will work with any graphical browser:
      <A HREF="/cgi-bin/imagemap/pic1">
      <IMG SRC="pic1.jpg" USEMAP="maps.html#map1" ISMAP></A>

      Clicking here will take you to a page with an error message if
      you don't have client-side image map support:
      <A HREF="no_csim.html">
      <IMG SRC="pic2.jpg" USEMAP="maps.html#map2"></A>   

      You can only click here if your browser supports client-side
      image maps: <IMG SRC="pic3.jpg" USEMAP="maps.html#map3">

   The following example shows the use of a map in the same file as
   the image:

      <IMG SRC="picture.jpg" USEMAP="#mymap">

   The following example defines a simple map which describes an
   image with a circle in the middle overlapping two large
   rectangles:

      <MAP NAME="welcomemap">
      <AREA SHAPE=CIRCLE COORDS="50,50,40" HREF="about_us.html"
            ALT="About our company">
      <AREA SHAPE=RECT COORDS="0,0,100,50" HREF="products.html"
            ALT="Our products">
      <AREA SHAPE=RECT COORDS="0,51,100,100 HREF="technology.html"
            ALT="Technology for the next century">
      </MAP>

3. References

   [1] T. Berners-Lee, D. Connolly.  "HyperText Markup Language
       Specification - 2.0" Internet-Draft (work in progress),
       June 16, 1995.

   [2] J. Seidman, "An HTML Extension to Support Client-Side Image
       Maps"  The Second Internation WWW Conference '94 Advance
       Proceedings, pp 927-930.

   [3] "Standard Generalized Markup Language"  ISO Standard 8879:1986
       Information Processing Text and Office Systems.

   [4] T. Berners-Lee, R. T. Fielding, H. Frystyk Nielsen,
       "Hypertext Transfer Protocol -- HTTP/1.0" Internet-Draft
       (work in progress), March 8, 1995.
       
4. Author's Address

   James L. Seidman
   jim@spyglass.com
   Senior Software Engineer
   Spyglass, Inc.
   1230 East Diehl Road
   Naperville, IL 60563

1
2	INTERNET-DRAFT James L. Seidman
3	<draft-ietf-html-clientsideimagemap-01.txt> Spyglass, Inc.
4	Expires SIX MONTHS FROM---> August 8, 1995
5
6	A Proposed Extension to HTML : Client-Side Image Maps
7
8	Status of this Memo
9
10	This document is an Internet-Draft. Internet-Drafts are working
11	documents of the Internet Engineering Task Force (IETF), its areas,
12	and its working groups. Note that other groups may also distribute
13	working documents as Internet-Drafts.
14
15	Internet-Drafts are draft documents valid for a maximum of six
16	months and may be updated, replaced, or obsoleted by other
17	documents at any time. It is inappropriate to use Internet-
18	Drafts as reference material or to cite them other than as
19	"work in progress."
20
21	To learn the current status of any Internet-Draft, please check
22	the "1id-abstracts.txt" listing contained in the Internet-
23	Drafts Shadow Directories on ds.internic.net (US East Coast),
24	nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or
25	munnari.oz.au (Pacific Rim).
26
27	Distribution of this document is unlimited. Please send
28	comments to the HTML working group (HTML-WG) of the
29	Internet Engineering Task Force (IETF) at <html-wg@oclc.org>.
30	Discussions of the group are archived at
31	URL: http://www.acl.lanl.gov/HTML_WG/archives.html.
32
33	Abstract
34
35	The markup language known as "HTML/2.0" provides for image maps.
36	Image maps are document elements which allow clicking on different
37	areas of an image to reference different network resources, as
38	specified by Uniform Resource Locators (URIs). The image map
39	capability in HTML/2.0 is limited in several ways, such as the
40	restriction that it only works with documents served via the "HTTP"
41	protocol, and the lack of a viable fallback for users of text-only
42	browsers. This document specifies an extension to the HTML
43	language, referred to as "Client-Side Image Maps," which resolves
44	these limitations.
45
46	Table of Contents
47
48	1. Introduction
49	1.1 Purpose
50	1.2 Overall Operation
51	2. Client-Side Image Map Extension
52	2.1 Syntax
53	2.2 Required Changes to HTML/2.0 DTD
54	2.3 Backwards Compatibility
55	2.4 Examples
56	3. References
57	4. Author's Address
58
59
60	1. Introduction
61
62	1.1 Purpose
63
64	Image maps are an important feature of the point-and-click
65	interface which makes the World Wide Web so popular. The most
66	common use of image maps is to allow users to access different
67	documents by clicking on different areas in an image.
68
69	There are several limitations of the current image map
70	implementation as it applies to this use. First, it only works
71	over the HTTP protocol, making it unusable for reading local files
72	or files accessed via alternate protocols. Second, a server
73	transaction is required merely to determine where the link is
74	directed. This can degrade performance noticeably when accessing
75	distant sites. Third, unlike for normal links, there is no way for
76	a browser to provide visual feedback to the user showing where a
77	portion of an image map leads before the user actually clicks on
78	it. Lastly, the method for specifying the active regions of image
79	maps is server-dependent, compromising portability of documents.
80	This extension to support client-side image maps addresses these
81	issues.
82
83	It is proposed that this extension be included in a future revision
84	of the HTML specification.
85
86	1.2 Overall Operation
87
88	Client-side image maps work by placing a complete representation of
89	the active areas of an image, including their shape, size, and
90	destination (URI), into an SGML-compliant textual form. This
91	markup may also optionally include a textual description for
92	each area for display on non-textual browsers. This
93	representation, or "map," is given a name to identify it.
94
95	When an image is included in an HTML document, it may include an
96	attribute specifying a map to use. The map may contained in the
97	same file which references the image, but this it not required.
98	If the map is in a different file, a URI to that file must be
99	provided.
100
101	The browser will parse the map and remember the contents. When the
102	user clicks on the map, the browser will match up the location with
103	the specified destination for that location and access that URI.
104	In the case of a non-graphical browser, the browser could display
105	the textual descriptions for each area instead of the image.
106	Clicking on a given textual description would then go to the
107	associated destination.
108
109
110	2. Client-Side Image Map Extension
111
112	2.1 Syntax
113
114	Adding a USEMAP attribute to an IMG element indicates that it is a
115	client-side image map. The USEMAP attribute can be used with the
116	ISMAP attribute to indicate that the the image can be processed as
117	either a client-side or server-side image map. The argument to
118	USEMAP specifies which map to use with the image, by specifying the
119	URI for the file containing the map, followed by a '#', followed by
120	the name of the map. If the argument to USEMAP starts with a '#',
121	the map is assumed to be in the same document as the IMG tag. The
122	presence of a USEMAP attribute overrides the effect of an enclosing
123	anchor (A) element.
124
125	The different regions of the image are described using a MAP
126	element. The map describes each region in the image and indicates
127	where it links to. The basic format for the MAP element is as
128	follows:
129
130	<MAP NAME="name">
131	<AREA [SHAPE="shape"] COORDS="x,y,..." [HREF="reference"]
132	[NOHREF] [ALT="alt"]>
133	</MAP>
134
135	The NAME attribute specifies the name of the map so that it can be
136	referenced by an IMG element. Each AREA element contained inside
137	the map element specifies a single clickable area of the image.
138	The SHAPE attribute gives the shape of this area. Possible shapes
139	are "RECT", "CIRCLE", and "POLYGON", which specify rectangular,
140	circular, and polygonal regions respectively. If the SHAPE tag is
141	omitted, SHAPE="RECT" is assumed.
142
143	The COORDS tag describes the position of an area, using image
144	pixels as the units with the origin at the upper-left corner of the
145	image. For a rectangle, the coordinates are given as
146	"left,top,right,bottom". The rectangular region defined includes
147	the lower-right corner specified, i.e. to specify the entire area
148	of a 100x100 image, the coordinates would be "0,0,99,99".
149
150	For a circular region, the coordinates are given as
151	"center_x,center_y,radius", specifying the center and radius of the
152	circle. All points up to and including those at a distance of
153	"radius" points from the center are included. For example, the
154	coordinates "4,4,2" would specify a circle which included the
155	coordinates (2,4) (6,4) (4,2) and (4,6).
156
157	For a polygonal region, the coordinates specify successive
158	vertices of the region in the format "x1,y1,x2,y2,...,xn,yn".
159	If the first and last coordinates are not the same then a segment
160	is inferred to close the polygon. The region includes the
161	boundary lines of the polygon. For example, "20,20,30,40,10,40"
162	would specify a triangle with vertices at (20,20) (30,40) and
163	(10,40). No explicit limit is placed on the number of vertices,
164	but a practical limit is imposed by the fact that HTML limits
165	an attribute value to 1024 characters.
166
167	The NOHREF attribute indicates that clicks in this region should
168	perform no action. An HREF attribute specifies where a click in
169	that area should lead. A relative anchor specification will be
170	expanded using the URI of the map description as a base, rather
171	than using the URI of the document from which the map description
172	is referenced. If a BASE tag is present in the document containing
173	the map description, that URI will be used as the base.
174
175	An arbitrary number of AREA tags may be specified. If two areas
176	intersect, the one which appears first in the map definition takes
177	precedence in the overlapping region. Multiple areas may share the
178	same destination to create composite shapes. Any portion of an
179	image which is not described by an AREA tag defaults to having no
180	action.
181
182	The ALT attribute specifies optional text which describes a given
183	area. A text-only browser can display the textual contents for
184	each area as a substitute for the image.
185
186	2.2 Required Changes to HTML/2.0 DTD
187
188	The required changes to the HTML/2.0 DTD to support this syntax
189	would be as follows:
190
191	Change the IMG element definition to be:
192	<!ELEMENT IMG - O EMPTY>
193	<!ATTLIST IMG
194	SRC %URI; #REQUIRED
195	ALT CDATA #IMPLIED
196	ALIGN (top\|middle\|bottom) #IMPLIED
197	ISMAP (ISMAP) #IMPLIED
198	USEMAP %URI; #IMPLIED
199	%SDAPREF; "<Fig><?SDATrans Img: #AttList>#AttVal(Alt)</Fig>"
200	>
201
202	Add the following new definitions:
203	<!ELEMENT MAP - - +(AREA)>
204	<!ATTLIST MAP
205	NAME %linkName; #REQUIRED
206	>
207
208	<!ELEMENT AREA - O EMPTY>
209	<!ATTLIST AREA
210	SHAPE (RECT\|CIRCLE\|POLYGON) RECT #IMPLIED
211	COORDS CDATA #REQUIRED
212	HREF %URI; #IMPLIED
213	NOHREF (NOHREF) #IMPLIED
214	ALT CDATA #IMPLIED
215	>
216
217
218	2.3 Backwards Compatibility
219
220	This extension is specifically designed to provide a variety of
221	fallback options for browsers which do not support it. These
222	options are based on the assumption that browsers will ignore any
223	attributes or elements which are not present in the HTML/2.0 DTD.
224
225	An document can be written so that a client-side image map can have
226	three different fallback behaviors. First, the document can use
227	the server-side image map capability, by specifying the ISMAP
228	attribute as well as USEMAP. In situations where this is possible,
229	the image map will work whether or not the browser supports the
230	client-side extension.
231
232	Second, clicking on the image can direct the user to a single URI,
233	regardless of where on the image he clicks. This is accomplished
234	by placing the image inside an anchor (A) element. The fallback
235	destination could provide the user with an error or a textual list
236	of destinations.
237
238	Lastly, the image can appear to not be a link at all (i.e. missing
239	whatever visual cues a browser provides to indicate a hyperlink).
240	This will be the result if the image element neither contains an
241	ISMAP attribute nor is inside an anchor.
242
243	2.4 Examples
244
245	The following three examples show markup demonstrating the three
246	fallback mechanisms described in section 2.3:
247
248	This image map will work with any graphical browser:
249	<A HREF="/cgi-bin/imagemap/pic1">
250	<IMG SRC="pic1.jpg" USEMAP="maps.html#map1" ISMAP></A>
251
252	Clicking here will take you to a page with an error message if
253	you don't have client-side image map support:
254	<A HREF="no_csim.html">
255	<IMG SRC="pic2.jpg" USEMAP="maps.html#map2"></A>
256
257	You can only click here if your browser supports client-side
258	image maps: <IMG SRC="pic3.jpg" USEMAP="maps.html#map3">
259
260	The following example shows the use of a map in the same file as
261	the image:
262
263	<IMG SRC="picture.jpg" USEMAP="#mymap">
264
265	The following example defines a simple map which describes an
266	image with a circle in the middle overlapping two large
267	rectangles:
268
269	<MAP NAME="welcomemap">
270	<AREA SHAPE=CIRCLE COORDS="50,50,40" HREF="about_us.html"
271	ALT="About our company">
272	<AREA SHAPE=RECT COORDS="0,0,100,50" HREF="products.html"
273	ALT="Our products">
274	<AREA SHAPE=RECT COORDS="0,51,100,100 HREF="technology.html"
275	ALT="Technology for the next century">
276	</MAP>
277
278	3. References
279
280	[1] T. Berners-Lee, D. Connolly. "HyperText Markup Language
281	Specification - 2.0" Internet-Draft (work in progress),
282	June 16, 1995.
283
284	[2] J. Seidman, "An HTML Extension to Support Client-Side Image
285	Maps" The Second Internation WWW Conference '94 Advance
286	Proceedings, pp 927-930.
287
288	[3] "Standard Generalized Markup Language" ISO Standard 8879:1986
289	Information Processing Text and Office Systems.
290
291	[4] T. Berners-Lee, R. T. Fielding, H. Frystyk Nielsen,
292	"Hypertext Transfer Protocol -- HTTP/1.0" Internet-Draft
293	(work in progress), March 8, 1995.
294
295	4. Author's Address
296
297	James L. Seidman
298	jim@spyglass.com
299	Senior Software Engineer
300	Spyglass, Inc.
301	1230 East Diehl Road
302	Naperville, IL 60563
303