Capabilities, Metadata and Adaptation Architectures

T-110.456 Next Generation Cellular Networks

Immo Heino

Content

• Adaptation and delivery context• Methods for describing capabilities and

preferences• Adaptation architectures• Summary

Adaptation and delivery context• Goals of content negotiation/adaptation – best efforts to

provide: Device independence Personalization

• Elements needed for content negotiation /adaptation: A way to describe attributes of the data source A way to describe capabilities & preferences of data requester Naming & registration schemes for labeling the attribute sets Frameworks (protocols & algorithms) to exchange and

process attributes

• Delivery context: A attribute set that characterizes the capabilities of the access

mechanism, the preferences of the user and other aspects of the context into which the content is to be delivered

General adaptation model

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Adaptation Rules

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• Picture source: W3C DIWG

Some characteristics of delivery context

• User interaction methods Presentation and capturing modalities

• User agent capabilities Scripting, MIME types capabilities

• Connections Networks, protocols, bandwidth, latency

• Location and localization Geographic location, proximity, languages, time

• Use environment Noise, light

• Level of discourse Verbosity, content detail

• Trust Privacy and security

Approaches to describe delivery context

• WWW Consortium (W3C) HTTP headers & negotiation CSS Media Queries CC/PP DPF SMIL

• Open Mobile Alliance (OMA) Wap UAProf

• IETF Conneg Media Feature Sets SIP

• ISO/IEC MPEG21

• Open source WURFL

HTTP headers & negotiation• Accept headers:

Accept : text/html (MIME types) Accept-Charset: iso-8859-5 (charset accepted) Accept-Encoding: gzip (preferred reply encoding) Accept-Language: en, fr=0.5 (preferred by user)

• User agent string: User-Agent: Nokia6630/1.0 (2.3.129) SymbianOS/8.0

Series60/2.6 Profile/MIDP-2.0 Configuration/CLDC-1.1• Server driven negotiation vs. HTTP 1.1 agent driven

negotiation Server determines which alternate to send to a user agent as

a result of examining the user agent’s request header fields Server gives a list of available presentations, User Agent is

responsible for selecting most appropriate content

HTTP headers & negotiation (cont.)

• Pros: Already used in practice

• Cons: User agent string format not standardized User agent strings are not officially available or maintained ( a

list of mobile UA agents strings: http://www.zytrax.com/tech/web/mobile_ids.html)

Limited capability to describe user preferences (no support for dynamic attributes/properties)

Agent driven negotiation delay (multiple request-response round trips)

Numerous proprietary HTTP headers are already used for content negotiation

CSS2/CSS3 Media Queries• HTML4 + CSS2 supports media-dependent style sheets

tailored for different media types <link rel="stylesheet" type="text/css" media="screen"

href="sans-serif.css"> <link rel="stylesheet" type="text/css" media="print" href="serif.css">

@media screen { * { font-family: sans-serif } } • CSS3 Media Queries = media type + media feature

expressions to limit the scope of the style sheets E.g. declares what kind of media types a style sheet is suitable

for <link rel="stylesheet" media="screen and (color)"

href="http://www.example.com/color" /> Several media queries can be combined

Comma = Logical Or, and = logical AND, only, not Associated style sheets applied (by User Agent) when

matching is true, otherwise ignored

CSS2/CSS3 Media Queries• Pros

Compatibility with current XML syntaxes Style sheets already supported (?) Proposed Media Features (CSS3) extends the control of

content presentation (related to IETF Conneg’s work) Width,height,color,resolution,scan, grid etc..

• Cons Coarse CSS2 media types (“aural”, “braille”, “handheld”,

“print”,”projection”, “screen”, “tty”, “tv”) CSS3 not supported yet with current browsers (limited support

with Opera 7, Mozilla 1.7, “IE Exploder” ?) Support for user preferences / non static attributes? Work in progress since 2002

CC/PP• W3C's Composite Capability/Preference Profiles is a framework:

for defining delivery contexts ( vocabularies e.g. attribute sets) by using the Resource Description Framework (RDF) [CCPPStruct]

allows devices to pass a description of these characteristics to Web servers for use in content selection/adaptation (CCPPex)

• CC/PPStruct standardize the structure of profile information In practice CC/PP vocabulary is a structured set (components) of (unique)

attribute names and valid attribute data types (RDF /XML Schema) Each vocabularies are uniquely identified by a URI Additional specification of meaning of attributes and attribute values is needed

• CC/PPEx standardize the exchange protocol Exchange of CC/PP refence profiles (as a URI) or profile diffs (inline XML ) HTTP extension framework (RFC2274) use was recommended but not

actually used (nor functionally equivalent W-HTTP) WSP used instead

WAP UAProf• The Open Mobile Alliance’s (formerly known as the WAP

Forum) CC/PP based vocabulary (CC/PP application) for describing static characteristics of mobile phones:

Hardware Platform: e.g., screen size, type of IO methods etc. Software Platform: operating system, supported markup

languages, supported media codecs etc. Network characteristics: bearer information Browser User Agent WAP characteristics: WML browsers WAP capability Push characteristics

• Virtually all CC/PP capable devices use UAProf • UAProf defines how to include profile information in WSP or

HTTP requets

Dynamic Properties Framework (DPF)

• Device configuration, user preferences and environmental conditions can vary dynamically

• W3C Multimodal Interaction Framework (abstract framework) Interaction manager —the logical component that coordinates data and manages

execution flow from various input and output modality component interface objects System & Environment - component enables the interaction manager to find out about

and respond to changes in device capabilities, user preferences and environmental conditions

Dynamic Properties Framework (cont.)

• Dynamic Properties Framework provides: the dynamic access (an DOM based interface) to a

hierarchy (a tree) of properties representing the current device capabilities, device configuration, user preferences and environmental conditions (related to MIF system & environment)

a mechanism to both query and update persistent (static) and transient (dynamic) properties

Properties raise events to notify changes to property values

• Complementary to CC/PP• Work has just started in 4Q/2004

IETF Conneg – MFS,BCP• Media Feature Tags (MFS), RFC 2506, 2533

allows complex descriptions of capabilities and preferences by allowing individual predicates to be combined using Boolean expressions in MIME-type definitions

An algorithm and a basic implementation of feature set matching is also presented

• Media Feature Tag Registration Procedure (BCP), RFC 2506 Handling of tag namespaces

IETF General Tree, Global tree (g.org-X.xxx) URI tree enables the sharing of media feature tags without registration (u.org.xxx)

• Example : Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="break" Content-features: (& (pix-x<=800) (pix-y<=600)       (|  (& (type=”text/html”) (charset=iso-8859-1)             (color=limited) )           (& (type=”text/plain”) (charset=US-ASCII) )           (& (type=”image/gif”) (color=mapped) )           (& (type=”image/jpeg”) (color=full) ) ) )

IETF Conneg – MSF,BCP (cont.)

• Pros: Based on solid principles (predicate calculus) Extendable Protocol independent Non-verbose (vs. XML-style tagging)

• Cons: Sender oriented approach (provides content media

information that augments basic MIME content type information)

Not actually used in practice (?)

MPEG21, SMIL, SIP etc..• MPEG-21 Multimedia Framework Digital Item Adaptation (DIA):

Descriptions of the environment (terminal, networks, user) focus on video, audio and image (requantization, wavelet and spatial size

reduction etc..)• SMIL (Synchronous Multimedia Integration Language) content control module

for runtime content choices and optimized content delivery priorities for different media objects Predefined Test Attributes & additional test-attributes (system-bitrate,

system-screen-size, system-screen-depth) media objects to be preloaded (as bandwidth allows) to improve presentation

quality.

• SIP (Session Initiation Protocol) provides a mechanism for user agents to negotiate the media types they can accept in message bodies

a user agent can announce the MIME media types it supports to another user agent.

SDPng (Session Description Protocol) for content negotiation (proposed IETF RFC in 2001)- related to work of IETF Multiparty Multimedia Session Control

Wireless Universal Resource File (WURFL)

• Standard like UAProf is endorsed by many in theory, but not enough in practice, which makes it hard to rely on:

infrastructure to set up UAProf profiles ? There is no guarantee that the info in UAProf are accurate

• the WURFL file contains information regarding wireless devices' configurations, capabilities and features

Open-source project and intended for developers working with the WAP environment.

Hundreds of possible properties to describe static properties (over 300)

contains over 1,500 devices XML based (human readable, machine interpretable)- Current size 2.5 MB The WURFL framework includes tools, utilities, and libraries to parse

and query the XML data• http://wurfl.sourceforge.net

Adaptation architecture models

• Architecture alternatives at the destination (client side) at the intermediary (proxy) at the source (server side)

• Dynamic vs. static adaptation Adaptation based on predefined profiles (static

versioning of the content) Adaptation on demand (“on the fly”)

Client side adaptation

• Picture source: W3C DIWG

Client side adaptation (cont.)

• Benefits Has full information on own capabilities, user preferences and

usage context Always has up-to-date information Can use information that could not be revealed to server (due

to privacy issues) Is not limited to what has been standardized

• Drawbacks Requires terminal processing resources (CPU, battery life) If dummy origin server, needless traffic (especially in mobile

networks !)

Intermediate (proxy) adaptation

• Picture source : W3C DIWG

Intermediate (proxy) adaptation

• Benefits: Moves computation from the client site to the proxy Complex transformations possible (image & video transcoding

etc..) Dedicated services possible (versatility)

Reduces the volume of data transferred to the client • Drawbacks:

Possible bottleneck No control for origin data (legal issues ?) nor terminal behavior Infrastructure maintenance (profile databases)

Server side adaptation

• Picture source: W3C DIWG

Server side adaptation (cont.)

• Benefits: Full control to the content (content modularization) Pre calculated content representations possible

(static adaptation) as well as dynamic adaptation

• Drawbacks: Infrastructure maintenance (profile databases) Storing content locally usually “locks it down” to a

specific adapted form (static adaptation)

Summary

• Adaptation/content negotiation is a very complex issue Moving target: terminal devices and the network infrastructure Variation of media types Changing (dynamic) properties of delivery context

• No single capability/metadata standard will be adequate or dominant

Due to diversity of standardization bodies ? Several overlapping work with metadata in progress or ended Standards will be only partially supported, manufacturer

specific extensions etc..?• Suitable adaptation architecture depends on application,

media content and required level of adaptation

References• Device Independence

http://www.w3.org/2001/di/

• SMIL Content control http://www.w3.org/TR/1999/WD-smil-boston-19991115/content.html

• Media Queries http://www.w3.org/TR/css3-mediaqueries/

• IETF Conneg http://www.imc.org/ietf-medfree/index.html

• MPEG21 DIA http://www-vs.informatik.uni-ulm.de/proj/qos/drafts/m10996_SDPng04

06131704.pdf• CC/PP

http://www.w3.org/Mobile/CCPP/• DPF

http://www.w3.org/TR/DPF/