Implementing XPath for Wireless Devices, Part II

Grok Headline matches for Implementing XPath for Wireless Devices, Part II

Implementing XPath for wireless devices,
part II (XML.com)

Implementing XPath for wireless devices,
part II (XML.com) 07/18/2002 07:34 PM

Implementing XPath for wireless devices
(XML.org)

Implementing XPath for wireless devices
(XML.org) 06/07/2002 08:34 AM

Implementing XPath for Wireless Devices

Implementing XPath for Wireless Devices 06/06/2002 05:37 PM
In the first of a two-part series, we explore the implementation of XPath on wireless devices using the WAP family of standards.

Implementing CSS (Part 1)

Implementing CSS (Part 1) 06/05/2005 11:17 PM

One of the most interesting problems (to me at least) in browser layout engines is how to implement a style system that can determine the style information for elements on a page efficiently. I worked on this extensively in the Gecko layout engine during my time at AOL and I've also done a lot of work on it for WebCore at Apple. My ideal implementation would actually be a hybrid of the two systems, since some of the optimizations I've done exist only in one engine or the other.

When dealing with style information like font size or text color, you have both the concept of back end information, what was specified in the style rule, and the concept of front end information, the computed result that you'll actually use when rendering. The interesting problem is how to compute this front end information for a given element efficiently.

Back end information can be specified in two different ways. It can either be specified using CSS syntax, whether in a stylesheet or in an inline style attribute on the element itself, or it is implicitly present because another attribute on the element specified presentational information. An example of such an attribute would be the color attribute on the font tag. Both WebCore and Gecko use the term mapped attribute to describe an attribute whose value (or even mere presence) maps to some implicit style declaration.

A rule in CSS consists of two pieces. There is the selector, that bit of information that says under what conditions the rule should match a given element, and there is the declaration, a list of property/value pairs that should be applied to the element should the selector be matched.

All back end information can ultimately be thought of as supplying a declaration. A normal rule in a stylesheet that is matched has the declaration specified as part of the rule. An inline style attribute on an element has no selector and is simply a declaration that always applies to that element. Similarly each individual mapped attribute (like the color and face attributes on the font tag) can be thought of as supplying a declaration as well.

Therefore the process of computing the style information for an element can be broken down into two phases. The first phase is to determine what set of declarations apply to an element. Once that back end information has been determined, the second phase is to take that back end information and quickly determine the information that should be used when rendering.

WebCore (in upcoming Safari releases) has a really cool optimization that I came up with to avoid even having to compute the set of declarations that apply to an element. This optimization in practice results in not even having to match style for about 60% of the elements on your page.

The idea behind the optimization is to recognize when two elements in a page are going to have the same style through DOM (and other state) inspection and to simply share the front end style information between those two elements whenever possible.

There are a number of conditions that must be met in order for this sharing to be possible:
(1) The elements must be in the same mouse state (e.g., one can't be in :hover while the other isn't)
(2) Neither element should have an id
(3) The tag names should match
(4) The class attributes should match
(5) The set of mapped attributes must be identical
(6) The link states must match
(7) The focus states must match
(8) Neither element should be affected by attribute selectors, where affected is defined as having any selector match that uses an attribute selector in any position within the selector at all
(9) There must be no inline style attribute on the elements
(10) There must be no sibling selectors in use at all. WebCore simply throws a global switch when any sibling selector is encountered and disables style sharing for the entire document when they are present. This includes the + selector and selectors like :first-child and :last-child.

The algorithm to locate a shared style then goes something like this. You walk through your previous siblings and for each one see if the above 10 conditions are met. If you find a match, then simply share your style information with the other element. Such a system obviously assumes a reference counting model for your front end style information.

Where this optimization kicks into high gear, however, is that it doesn't have to give up if no siblings can be located. Because the detection of identical style contexts is essentially O(1), nothing more than a straight pointer comparison, you can easily look for cousins of your element and still share style with those elements.

The way this works is that if you can't locate a sibling, you can go up to a parent element and attempt to find a sibling or cousin of the parent element that has the same style pointer. If you find such an element, you can then drill back down into its children and attempt to find a match.

This means that for HTML like the following:

<table>
<tr class='row'>
<td class='cell' width=300 nowrap>Cell One</td>
</tr>
<tr class='row'>
<td class='cell' width=300 nowrap>Cell Two</td>
</tr>

In the above example, not only do the two rows share the same style information, but the two cells do as well. This optimization works extremely well for both old-school HTML (in which many deprecated presentational tags are used) and newer HTML (in which class attributes might figure more prominently).

Once the engine determines that a style can't be shared, i.e., that no pre-existing front end style pointer is available, then it's time to figure out the set of declarations that match a given element. It is obvious that for inline style attributes and mapped attributes that you can find the corresponding declaration quickly. The inline style declaration can be owned by the element, and the mapped attributes can be kept in a document-level hash. WebCore has a bit of an edge over Gecko here in that it treats each individual mapped attribute on an element as a separate declaration, whereas Gecko hashes all of the mapped attributes on an element as a single "rule." This means that Gecko will not be able to share the mapped attribute declaration for the following two elements:

<img width=300 border=0>
<img width=500 border=0>

WebCore creates three unique declarations and hashes them, one for a width of 300, one for a width of 500, and one for a border of 0. Gecko creates two different "rules," one for (width=300,border=0) and another for (width=500,border=0). As you can see in such a system, you will frequently not be able to treat the identical border attributes as the same.

Aside from this difference in mapped attribute handling, the two engines employ a similar optimization for quickly determining matching stylesheet rules called rule filtering. All rules that are potentially matchable by any element (i.e., that have the correct media type) are hashed based on the contents of the rightmost simple selector in the rule.

A selector in CSS can be either simple (meaning that all of the contents of that selector apply only to a single element) or compound (meaning that you may examine multiple elements like parents or siblings of that element). A compound selector is essentially a chain of simple selectors, so the following rule:

tr > td { color: blue }

has two simple selectors, tr and td. The rightmost simple selector in the rule is the one that we will use for the rule filtering optimization.

The rightmost simple selector falls into four categories.

(1) The selector uses an ID. (Example: #foo)
(2) The selector doesn't have an ID but uses a class. (Example: .foo)
(3) The selector has no class or ID but specifies a tag name. (Example: div)
(4) The selector specifies none of these things. (Example: *[disabled])

The rule is placed into one of four hashtables depending on which category it falls into. The idea behind these categorizations is to always filter out more specific information first. For example, if an element has a specific ID, then obviously any rules whose rightmost selector uses a different ID cannot match. Technically the last category can just be a list and not a hashtable, since those rules must always be examined by all elements.

Each hashtable, therefore, consists of a mapping from a given atomic string to a set of rules that match. The class attribute is exceptional in that you must put the rule into the hashtable multiple times if multiple class attributes are used.

When determining the set of rules that match a given element, you only examine rules that correspond to the correct hash entry based off your ID, classes and tag name. This optimization basically eliminates 95+% of the rules up front so that they need not even be considered during the matching process.

Each rule is then examined in detail, with all selectors being checked, to determine if it is a match, and the set of matches is collected. The set of matches can then be sorted by priority and specificity such that all the declarations are in the proper application order.

This brings us to the final phase of the style computation, which is taking the set of matches and quickly computing the appropriate front end style information. It is here that Gecko really shines. What I implemented in Gecko was a data structure called the rule tree for efficient storing of cached style information that can be shared *even when* two elements are not necessarily the same.

The idea behind the rule tree is as follows. You can think of the universe of possible rules in your document as an alphabet and the set of rules that are matched by an element as a given input word. For example, imagine that you had 26 rules in a stylesheet and you labeled them A-Z. One element might match three rules in the sheet, thus forming the input word "C-A-T" or another might form the input word "D-O-G."

There are several important observations one can make once you formulate the problem this way. The first is that words that are prefixes of a larger word will end up applying the same set of rules. All additional letters in the word do is result in the application of more declarations. Thus the rule tree is effectively a lexicographic tree of nodes, with each node in a tree being created lazily as you walk the tree spelling out a given word.

This system allows you to cache style information at each node in the tree. This means that once you've looked up the word "C-A-T-E-R-W-A-U-L", and cached information at all of the nodes, then looking up the word "C-A-T" becomes more efficient.

In order to make the caching efficient, properties can be grouped into categories, with the primary criterion for categorization being whether the property inherits by default. It's also important to group properties together that would logically be specified together, so that when a fault occurs and you have to make a copy of a given struct, you do so knowing that the other values in the struct were probably going to be different anyway.

Once you have the properties grouped into categories like the border struct or the background struct, then you can either store these structs in the rule tree or as part of a style tree that more or less matches the structure of the document. Inheritance has to apply down the style tree and tends to force a fault, whereas non-inherited properties can usually be cached in the rule tree for easy access.

WebCore doesn't contain a rule tree, but it is smart enough to refcount the structs and share them as long as no properties have been set in the struct. In practice this works pretty well but is not as ideal as the rule tree solution.

Enterprise Java Beans - Part 2,
Implementing Your First EJBs

Enterprise Java Beans - Part 2,
Implementing Your First EJBs 11/14/2003 03:33 AM
WebmasterBase Nov 14 2003 2:36AM ET

Where Do You Use Wireless Devices?

Where Do You Use Wireless Devices? 09/10/2004 10:43 AM
If you ever needed more proof that people use wireless devices to help them fill in the "empty" time when it used to be difficult to work or communicate, Harris Interactive has the study for you. They've found that a fair number of people use wireless devices in places that previously were pretty much off-limits towards anything productive: waiting in the drive-through at the fast-food place (22%), while driving (20%) and in the bathroom (15%). This isn't just talking about mobile data, but mobile phone conversations, which would make you think that the numbers should be higher. Of course, they are higher for the younger generation, with 30% of college students admitting they used wireless devices in the bathroom. Of course, whether or not this is a good thing probably depends on whether or not you're one of the people using wireless devices in these places.

Spy on CMU's wireless devices

Spy on CMU's wireless devices 11/13/2003 03:59 PM
Here's a real-time map of all the wireless devices using CMU's campus-wide network. Link (Thanks, Ophir!)

First 3G Wireless Devices for Canadians

First 3G Wireless Devices for Canadians 07/21/2004 09:36 AM
3G Jul 21 2004 1:52PM GMT

Wireless devices a DNC hazard

Wireless devices a DNC hazard 07/27/2004 12:56 AM

Direct and Related Links for 'Wireless devices a DNC hazard'

“There’s a gaping hole in the much-hyped security measures taken for this week’s Democratic National Convention: Thousands of wireless devices around the FleetCenter could be used as pawns in a cyberattack. Wireless security provider Newbury Networks Inc. of Boston issued that warning after detecting the heavy concentration of devices during a three-hour ‘war driving’ exercise through the city. Many of the unsecured wireless networks and 802.11 client cards were in a one-block radius of the…

Targus rolls out new wireless devices

Targus rolls out new wireless devices 07/26/2004 12:35 PM
Targus has introduced a new Wireless Multimedia Presenter and Wireless Calculator Keypad for notebook computers...

FCC Blocks Spam on Wireless Devices

FCC Blocks Spam on Wireless Devices 08/05/2004 02:31 PM
The FCC wants to stop spam from reaching your PDA and/or cell phone. It's a step in the right direction and much appreciated, but may not protect cell phones and PDAs from forwarded spam emails.

The Federal Communications Commission yesterday moved to prevent cell phones and personal digital assistants (PDAs) from becoming the next major frontier for e-mail spam.

The agency issued rules requiring marketers to have explicit permission from wireless-device users before they can be sent any commercial e-mail. And it urged the industry to develop technologies to prevent spam from overwhelming wireless devices the way it has swamped computer messaging.

"By prohibiting all commercial messages to wireless phones and PDAs absent affirmative consent from the consumer, Americans can now use their wireless devices freely, without being bothered by unwanted and annoying messages," FCC Chairman Michael K. Powell said in a prepared statement.

The rule covers a rapidly expanding array of Web-based e-mail services offered by wireless providers that enable customers to send and read messages via their phones or PDAs.

View: Complete Article
News source: The Washington Post

Read full story...

Cisco unveils wireless devices

Cisco unveils wireless devices 11/14/2003 09:08 AM
Computer Weekly Nov 14 2003 8:10AM ET

Wireless FireWire devices coming

Wireless FireWire devices coming 05/12/2004 09:55 AM
The 1394 Trade Association this week approved a new specification that enables companies to develop wireless FireWire products...

Wireless Devices Help Police Fight Crime

Wireless Devices Help Police Fight Crime 06/24/2004 09:25 PM
AP via Daily Press Jun 25 2004 1:12AM GMT

FCC Blocks Spam on Wireless Devices
(washingtonpost.com)

FCC Blocks Spam on Wireless Devices
(washingtonpost.com) 08/05/2004 07:04 AM
washingtonpost.com - The Federal Communications Commission yesterday moved to prevent cell phones and personal digital assistants (PDAs) from becoming the next major frontier for e-mail spam.

Ambient Devices Launches Wireless
DataCasting Kit

Ambient Devices Launches Wireless
DataCasting Kit 03/24/2005 04:27 AM
Ambient and Microsoft lead the trend to display glanceable information. [PRWEB Mar 24, 2005]

Re[2]: Denial of Service Vulnerability
in IEEE 802.11 Wireless Devices

Re[2]: Denial of Service Vulnerability
in IEEE 802.11 Wireless Devices 05/17/2004 01:39 PM
Jason Ostrom (May 15 2004)

Testing of Location-Capable 3G UMTS
Wireless Devices

Testing of Location-Capable 3G UMTS
Wireless Devices 12/02/2003 04:16 AM
3G Dec 2 2003 3:34AM ET

ParkerVision Intros D2D Wireless Chips
for Mobile Devices

ParkerVision Intros D2D Wireless Chips
for Mobile Devices 02/05/2005 09:51 PM
Power Pulse.Net Feb 4 2005 11:36PM GMT

Re: Denial of Service Vulnerability in
IEEE 802.11 Wireless Devices

Re: Denial of Service Vulnerability in
IEEE 802.11 Wireless Devices 05/15/2004 03:52 PM
Casper Dik (May 15 2004)

Denial of Service Vulnerability in IEEE
802.11 Wireless Devices

Denial of Service Vulnerability in IEEE
802.11 Wireless Devices 05/15/2004 02:44 PM
albatross_at_tim.it (May 15 2004)

New Wireless Chips Reduce Power
Consumption in Mobile Devices

New Wireless Chips Reduce Power
Consumption in Mobile Devices 02/01/2005 09:37 PM
Lockergnome Feb 1 2005 10:30AM GMT

IntelliTrack Adds Support for Wireless
Devices from American Microsystems Ltd.

IntelliTrack Adds Support for Wireless
Devices from American Microsystems Ltd. 02/01/2005 09:17 PM
IntelliTrack Inc., the leading manufacturer of affordable bar code tracking software, announced today that its entire product line now supports the American Microsystems Ltd. (AML) Wireless (RF) Terminal, model M7100. [PRWEB Jan 28, 2005]

Microsoft, Fiat Form Partnership on
Putting Wireless Devices in Vehicles

Microsoft, Fiat Form Partnership on
Putting Wireless Devices in Vehicles 07/15/2004 05:06 PM
Technology Review Jul 15 2004 9:42PM GMT

Telecom Italia CEO sees innovation in
design and features of wireless devices

Telecom Italia CEO sees innovation in
design and features of wireless devices 09/22/2004 02:49 PM
VENICE - One of Europe's biggest fixed-network operators is following the lead of its wireless counterparts in demanding a greater say in the design and service features of cordless phones and other wireless devices used in the home.

Ethernet to Serial- MOXA Wireless Device
Server Network RS-232, RS-422, RS-485
Devices

Ethernet to Serial- MOXA Wireless Device
Server Network RS-232, RS-422, RS-485
Devices 02/05/2005 09:05 PM
MOXA offers single and multi-port wireless device server for Serial-to-Wireless LAN applications [PRWEB Feb 4, 2005]

Siemens ICM WM Chooses Analog Devices
and TTPCom Wireless Technologies for
Next-Generation EDGE Modules

Siemens ICM WM Chooses Analog Devices
and TTPCom Wireless Technologies for
Next-Generation EDGE Modules 06/19/2004 02:50 AM
Leading manufacturer of wireless modules will use ADI’s Blackfin SoftFone for EDGE and TTPCom’s protocol software in new modules [PRWEB Jun 19, 2004]

Adesso Cuts the Cord with New Elegant,
Wireless Keyboards with Integrated
Cursor Control Devices

Adesso Cuts the Cord with New Elegant,
Wireless Keyboards with Integrated
Cursor Control Devices 02/01/2005 09:13 PM
New 2.4 GHz and Infrared wireless keyboard series feature integrated touchpad, trackball, or cursor pad [PRWEB Jan 31, 2005]

SplashData Launches SplashMoney 4.0 for
Palm OS Devices, Introducing Wireless
Online Banking for PDAs and Smartphones

SplashData Launches SplashMoney 4.0 for
Palm OS Devices, Introducing Wireless
Online Banking for PDAs and Smartphones 03/14/2005 05:26 PM
Financial management software also provides two-way synchronization with desktop PCs. [PRWEB Mar 1, 2005]

RegiSoft and SiSTeR cooperate to enable
the simple creation, formatting, and
delivery of Multi Media Messages for
wireless devices.

RegiSoft and SiSTeR cooperate to enable
the simple creation, formatting, and
delivery of Multi Media Messages for
wireless devices. 06/17/2004 03:25 AM
RegiSoft, creators of the World Trade Server™ middleware platform, and applications for m-commerce, and Silver Screen Tele-Reality (SiSTeR), creators of M-Plat, an online video editing and embedded voice-over platform, has signed an agreement to integrate and co-market their products to create an enhanced offering using their innovative technologies. [PRWEB Jun 17, 2004]

Q&A: Wireless LANs, part 2

Q&A: Wireless LANs, part 2 04/14/2004 06:31 AM
vnunet.com Apr 14 2004 11:09AM GMT

Wireless Attacks and Penetration Testing
(part 1 of 3)

Wireless Attacks and Penetration Testing
(part 1 of 3) 06/04/2004 05:57 AM

Wireless Attacks and Penetration Testing
(part 2 of 3)

Wireless Attacks and Penetration Testing
(part 2 of 3) 06/15/2004 09:51 AM

Wireless Attacks and Penetration Testing
(part 3 of 3)

Wireless Attacks and Penetration Testing
(part 3 of 3) 07/27/2004 09:29 AM

Device Server - Wireless Serial to
Ethernet Converter for RS232/422/485
Serial Devices

Device Server - Wireless Serial to
Ethernet Converter for RS232/422/485
Serial Devices 12/29/2004 05:50 AM
HelloDevice SS110 is a Wireless-enabled serial to ethernet converter for RS232/422/485 based serial devices. [PRWEB Dec 29, 2004]

Ori Amiga - Tour of mobile devices with
Visual Studio for Devices team

Ori Amiga - Tour of mobile devices with
Visual Studio for Devices team 09/25/2004 09:16 AM
Ori Amiga shows off all the devices that he has hanging out in his office (someone has to test Visual Studio and make sure it works great with all the devices).

AT&T Wireless slashing 1,900 jobs as
part of cost-cutting

AT&T Wireless slashing 1,900 jobs as
part of cost-cutting 11/14/2003 08:37 PM
SiliconValley.com Nov 14 2003 7:45PM ET

Barefoot Software Launch Australian
Swimsuit Edition-Free, a Free Mobile
Phone and Wireless Device Service for
Cardmate on Symbian Devices

Barefoot Software Launch Australian
Swimsuit Edition-Free, a Free Mobile
Phone and Wireless Device Service for
Cardmate on Symbian Devices 06/12/2004 02:48 AM
Barefoot Software Asia Limited (BSAL) is pleased to announce the launch Australian Swimsuit Edition-Free (ASE), via the Barefoot Software website (http://www.barefootsoft.com) for immediate download. ASE is a Cardmate application for mobile phones which is being launched for Free as a promotional application to end users who have a Symbian based mobile phone. ASE, the first Australian swimsuit model application for Smartphone devices in the World can initially be downloaded by users who have a Nokia (6600/3650/7650), Sony Ericsson P800/P900 and other compatible phones from the barefoot Web site. [PRWEB Jun 12, 2004]

Bitboys Introduces New Graphics
Processorsfor Wireless Devices - Small,
Smart and Efficient Processor Cores
Bring Advanced Graphics Capabilities to
Handheld Products

Bitboys Introduces New Graphics
Processorsfor Wireless Devices - Small,
Smart and Efficient Processor Cores
Bring Advanced Graphics Capabilities to
Handheld Products 08/10/2004 03:08 AM
(Los Angeles, California and Espoo, Finland – August 10th, 2004) -- Bitboys, a provider of graphics hardware solutions, today announced and demonstrated the company’s new graphics processor product line for wireless and embedded devices at SIGGRAPH 2004 in Los Angeles. [PRWEB Aug 10, 2004]
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Implementing XPath for Wireless Devices, Part II

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