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Lecture 4: Architectural Patterns – Part 2SGN-5226 Content Sharing Technologies and Services
23.9.2010
A detailed reference architecture for Web 2.0 Services
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Patterns we are going to study in detail
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1. The Service-Oriented Architecture Pattern2. The Software as a Service (SaaS) Pattern3. The Participation-Collaboration Pattern4 The Asynchronous Particle Update Pattern4. The Asynchronous Particle Update Pattern5. The Mashup Pattern6. The Rich User Experience Pattern7. The Synchronized Web Patterny8. The Collaborative Tagging Pattern9. The Declarative Living and Tag Gardening Pattern10. The Semantic Web Grounding Pattern11. The Persistent Rights Management (PRM) Pattern12. The Structured Information Pattern
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6. The Rich User Experience Pattern6. The Rich User Experience Pattern
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Business Problem
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• Original websites were based on static content (e.g. Web pages, .pdf files), typically mapped to real world artifacts (e.g. Brochures)
• However in the real world those artifacts are only part of the wholeHowever, in the real world, those artifacts are only part of the whole interaction
• Stepping into a car dealer, gives to the user much more than simply a brochure (talking to the seller, touching the car, talking to other customers)
• Those interactions are difficult to bring to the electronic domain
• For the electronic interaction to match the human-to-human interaction, the application has to be dynamic, and contextually engage the user
• Amazon’s ”customers who bought this item also bought...”• Customize your own car...• Wow factor...
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Context
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Usable anywhere that a users needs to interact richly with an application, optimizing visual information and information relevance
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Derived Requirements
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• Contextually specialized experience• E.g. taking the user automatically to the corresponding national page• Centering a map to a user’s approximate location (based on IP address)
• Being able to render a variety of content/media, for rich user experience (RUE)
F t d i UI d i• Fast and responsive UI -> good experience• Mashing up capabilities at the client• Support both online and offline states• Easy to deploy on multiple platformsEasy to deploy on multiple platforms
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Static Structure and Dynamic Behavior
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Developers should clearly identify the different states and interactions that might occur between the user and the system. Create a “story board”, map to different Graphical User Interface elements, etc.
Simple example: an application that is linked to a user account, potentially has the following states that need to be considered:
• Normal, Password Lost, Username Lost, Both Lost, Password Lost and email Changed Unregistered User Phishing Double User RegistrationChanged, Unregistered User, Phishing, Double User Registration…
• Now think more complicated scenarios…
• Advice: short forms to fill-in, validating forms, careful when to reset a whole form incorporating elements that prevent users from enteringwhole form, incorporating elements that prevent users from entering incorrect data, presenting all relevant data to the users in a given context, …
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Static Structure and Dynamic Behavior
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Good example of RUE
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Implementation
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Key issues to consider:• Team should model the whole system (use cases, views, sequence
diagrams, data models, etc)
• Try to consider the application also independent of technology• Technologies change, but business patterns are more stable
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Business Problem Resolved
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The simple login example:• Normal, Password Lost, Username Lost, Both Lost, Password Lost and email
Changed, Unregistered User, Phishing, Double User Registration…
• Consider also OpenID, for “outsourcing” the complexity• We will study OpenID in a future lecture
• This was only a small example. RUE can be applied in a variety of otherThis was only a small example. RUE can be applied in a variety of other applications and scenarios
• iTunes• Customize my car• Decorate my house• Decorate my house• …
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Consequences
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• Provide a positive feeling to the users
• Get users to come back, easily register, comment, contribute
• Viral marketing, get the people to suggest your site to others• Example: http://vimeo.com/4281939
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7. The Synchronized Web Pattern7. The Synchronized Web Pattern
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Business Problem
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Most web-based services are created for being accessed/experienced while having broadband connection
However users (e g mobile users) might not have always-on connectivityHowever, users (e.g. mobile users) might not have always on connectivity• Think flying by airplane, in a tunnel by train, ...
Also, user data is distributed (and duplicated) among different services, and not synchronized.
• User has to update his/her data in multiple places
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Context
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Typically applies when an application has a desktop and a network (service) component
• Data needs to be synchronized
Variation of the Software As A Service pattern, but more focused on keeping state synchronized
Al li h th li ti i d t b d i ff li dAlso, applies when the application is supposed to be used in off-line mode
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Derived Requirements
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• Need for replication and synchronization services• A local web application server and persistent data storage
• Set rules for the synchronization process, conflict handling, etc. (e.g.Set rules for the synchronization process, conflict handling, etc. (e.g. usage of timestamps)
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Static Structure
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Static Structure
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Static Structure
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Static Structure
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AJAX has been used to build synchronization functionality into Rich Internal Application
Zimbra has been one of the first service to showcase a rich AJAX webZimbra has been one of the first service to showcase a rich AJAX web application synchronized
• http://www.youtube.com/watch?v=T8bvimEZPhU
G il ff liGmail off-line access• http://www.youtube.com/watch?v=cOAZaIaeIrI
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Business Problem Resolved
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Richer user experience, as applications (desktop, mobile, etc.) and the web are synchronized
Software as a Service even more appealing as it can be used in off-lineSoftware as a Service even more appealing, as it can be used in off line situations
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Consequences
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• Take web applications offline• Take client application online• Move between services, as data could be (theoretically) synchronized
• E g move everything from Gmail to Yahoo! main scenario• E.g. move everything from Gmail to Yahoo! main, scenario
• Data moving among services• When you do something in one service, it appears at others, so you don’t have
t t tito repeat actions
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Consequences
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• Data moving among services• When you do something in one
service, it appears at others, so you don’t have to repeat actions
• Example:• Data from Dopplr appearing on
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8. The Collaborative Tagging Pattern8. The Collaborative Tagging Pattern
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Business Problem
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Searching resources on the Internet, is typically based on search terms, which are compared against terms in a metadata index
Typically metadata index is built on resourced being tagged a small numberTypically metadata index is built on resourced being tagged a small number of people
• E.g. tags on a photo
Th ll h h h f i / i iThe smaller the group, the more chances of inaccurate tags / omissions
• Reminder: Tagging = apply/associate a label to an object, declaring what it representsp
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Context
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Collaborative tagging adds natural language (from the community) to searching and indexing mechanisms
Allows better searching/results without the need to extensive hierarchicalAllows better searching/results without the need to extensive hierarchical metadata annotations
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Derived Requirements
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• Resources must be associated with metadata, allowing people to extend them and rank their relevance
• Tags must have natural language to be meaningfulTags must have natural language, to be meaningful
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Static Structure
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Resources (e.g. photos) are examined by people and according to their own interpretation of what they represent, they add tags
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Dynamic Behavior
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Business Problem Resolved
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• The more users populating the tags, the more effective the search
• Google spell check works this way• Not based on a static dictionary but based on commonly searched terms• Not based on a static dictionary, but based on commonly searched terms
• Google Image Labeler is a great example of collaborative photo tagging• http://images.google.com/imagelabeler/
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Consequences
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• Some people have argued that the tagging (folksonomy) approach are not to be trusted, due to the lack of formalized ontology (i.e. higher level formal logic)
• The “most relevant” approach, might be faulty, because you do not know for which other people it was most relevant to
H it t k fi It th t th tt f• However, it seems to work fine… It appears that there are patterns of use in the folksonomy approach that have consistent results, at large groups of people
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9. The Declarative Living and Tag Gardening Pattern9. The Declarative Living and Tag Gardening Pattern
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Business Problem
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As we discussed with tags, people can declare objects, state their opinion, etc.
Conclusions cab be drawn from the aggregation of those declarationsConclusions cab be drawn from the aggregation of those declarations
Until now, there was no way to collectively use those declarations
Specific services try to aggregate those user preferences, as tags, and provide rich semantic information (tag gardening)
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Context
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Applies where declarations are harvested for some computer functionality• An artificial intelligence component helps to inference a conclusion
E.g. People blogging with their location -> declarative livingE.g. People blogging with their location declarative living
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Derived Requirements
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• Need for mechanism/UI that lets the users make conscious declarations• E.g. Twitter, Delicious, Facebook status updates
• First collect data, then build tag gardeningFirst collect data, then build tag gardening• You cannot analyze the data, if there are no tags at first place
• How to split and aggregate data to and from multiple machines
• Performance
• ScalingScaling
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Static Structure
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Declarative living: Very similar to Collaborative tagging, but specific to the human making the declarations (Collaborative tagging agnostic to the “actor”)
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Static Structure
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Tag gardening
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Implementation
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Many commonalities with Collaborative Tagging
In Tag Gardening, data can be visualized (e g to a tag cloud)(e.g. to a tag cloud)
Key issues to consider:Gi th f t th t t h ld t t k d l ti li i• Given the fact that a system should try to make declarative living as easy as possible (so that as much data as possible is gathered), related APIs should be as simple as possible
• SOAP is considered over-complex. Consider REST
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Business Problem Resolved
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Declarative living allows more user data to be gathered at services. With the usage of microformats, Twitter manages to extract even more specific data from the user statements
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http://www.mentalfloss.com/blogs/archives/31487
Consequences
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Minimizing complexity for tagging (at infrastructure and API) the declarative living and tag gardening will bring more users to the service
• More users = more attention = more chances for monetization
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10. The Semantic Web Grounding Pattern10. The Semantic Web Grounding Pattern
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Business Problem
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An organization has millions of data elements, aggregated from multiple sources.
Searching functionality is provided but due to the large amounts of dataSearching functionality is provided, but due to the large amounts of data, relevance is not always good
• Sorting and ranking helps, but slow and inefficient (due to the amount of data)
S f f ti d l ti b t th h l• Some form of semantic declaration about the resources can help• Declarations can come from a single or multiple sources
• With Semantic Web Grounding, an intermediate step helps in inspecting the claims (made about the resources) and compares them to real-world patterns of interaction with the resource
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Context
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Can be applied where there is large number of resources, linked to some declarations about what they represent
Declarations are not based on some pre-agreed scemanticsDeclarations are not based on some pre agreed scemantics• Tags or lables
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Derived Requirements
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Need for mechanism for allowing claims to be made about resources
Resources must be uniquely identified
There is a needed for a mechanism to get feedback about those claim-resource links, based on some real-world effects observations
Need for an adaptive mechanism that is influenced by the claims vs. the real-world observations
E g a search engine monitoring which of the provided links (which areE.g. a search engine monitoring which of the provided links (which are results to a search query) are clicked. And (using cookies) measuring if a user is coming back to the search page, once visiting an external link
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Static Structure
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Implementation
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A simple word-tagging mechanism in which any interacting party (e.g. a user) can declare which tags are relevant to the resource
A post-processing analysis is using this data to recalculate the relevanceA post processing analysis is using this data to recalculate the relevance
More complicated example: The search engine that monitors the visitor interactions
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Business Problem Resolved
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This pattern inserts an adaptive dynamic layer to the semantic web and behavior tracking, by grounding semantic claims in an real-world interaction observation
As the system is used more and more, the relevance of the results are increasing
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Consequences
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Applications still rely on individual users
Issues: different cultures, language, etc.
Those systems work for the majority of the people, but there is always a minority that is not served well.
• Adding to the mechanism some knowledge about the individual (requesting) i ht i th ltuser, might improve the results
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11. The Persistent Rights Management (PRM) Pattern11. The Persistent Rights Management (PRM) Pattern
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Business Problem
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PRM wider than DRM (Digital Rights Management)
As digital assets are distributed on the Web, it is difficult to enforce policies to them as in the real world Things are more difficult when multipleto them, as in the real world. Things are more difficult when multiple copies exist
Examples• Somebody might be working with an older version of a digital asset,
because he is not aware that a newer version exists• Somebody released a document that needs to be recalled, erasing all
traces of its existence
Placing resources under a secure domain and requiring authentication is not a solution, as there is no control outside the secure domain
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Business Problem
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Context
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Applies in an environment where the owner of the digital assents wants to keep and exercise post-distribution management rights of the data
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Derived Requirements
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• Digital assets must be linked to a centralized control policy
• No application/client should be able to ignore/bypass the policy
• The applications should have the needed information and means of enforcing the policies
• E.g. if authentication of a user is needed via a corporate directory, the li ti h ld b bl t d tili itapplication should be able to access and utilize it
• The policies should be dynamically changeable by the asset owners
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Static Structure
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Each digital asset needs to be “wrapped” with data that relays information about the policy information
• How was the asset encrypted• Where to obtain the decryption keysyp y• Where is the policy located• What data needs to be collected from the user• …
Policy Digital AssetPolicy Repository
Policy
Digital Asset
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Policy wrapper
Dynamic Behavior
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Implementation
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Key issues to consider:• Link between the clients and policy server would be a potential attack
point
• Wrapper should be accessible, inspectable by the clients, even if actual asset is protected
• Strong encryption to protect against brute-force attacks
• Authentication of users should be typically linked to the policy server
• Asset owners should have a way of changing the policies of deployed assets
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Business Problem Resolved
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• Encryption of core assets, and policy wrapper, allows protection of assets
• Dynamic asset management is possible, if supported by system
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Consequences
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• Problem is an application is not aware of the system and does not “understand” the wrapper
• Issues with off-line access (as no link to policy server)Issues with off line access (as no link to policy server)
• Issues with searching (as assets are not accessible by search bots)• Consider core metadata outside the encrypted asset
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12. The Structured Information Pattern12. The Structured Information Pattern
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Business Problem
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• Most of the data on the Internet is unstructured content• Mainly in HTML• HTML includes information about the presentation, but not details on where to
find specific parts of information, within a page
• Scraping data is possible (e.g. parsing a document, and trying to “guess” the location of the data), but very fragile
• If the format of the document changes, the parsing might failIf the format of the document changes, the parsing might fail
• E.g. How do we take out of cnn.com page the main news title?
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Context
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Data stored in HTML is difficult to reuse
Changing the existing HTML creation processes is also difficult
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Derived Requirements
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• Authors need a language to markup (tag) various parts of their content, in such a way that applications can consistently retrieve the specific parts of the data
• I.e. allow creation of declarations at the inner structure of the document
• The declarations must have meaning also for the consumers
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Static Structure
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Dynamic Behavior
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• Once author has prepared the content, it can be marked with microformats to allow addressing in fine-grained level
• Clients access the content (e g HTML) with the standard way (HTTPClients access the content (e.g. HTML) with the standard way (HTTP GET)
• As content is parsed, the special tags are identified, and the client is id d ith th ifi d t f f thprovided with the specific data, for further usage
• Example, once an <object> element is parsed, the browser is instructured to launch a plug-in (e.g. Flash player) to consume the relevant p g ( g p y )content/data
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Implementation
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Key issues to consider:• Microformat tags should not conflict with main mark-up language
• Usage of namespaces is a solution
• Before creating a syntax, create a formal group that would support it
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Business Problem Resolved
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Microformats allow direct access/referencing to specific segments of content
Allows other patterns (e g mashup) to be implemented in a commonAllows other patterns (e.g. mashup) to be implemented in a common manner
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Consequences
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Carefully consider the forward compatibility, when embedding microformats in content
• E.g. future conflicts, collisions of syntax, etc/
Carefully consider level of granularity• E.g. an address can be split in many level (country, city, region, area, postal
code, street name, street direction, number…)• Consider future extension possibilitiesConsider future extension possibilities
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Patterns
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1. The Service-Oriented Architecture Pattern2. The Software as a Service (SaaS) Pattern3. The Participation-Collaboration Pattern4 The Asynchronous Particle Update Pattern4. The Asynchronous Particle Update Pattern5. The Mashup Pattern6. The Rich User Experience Pattern7. The Synchronized Web Patterny8. The Collaborative Tagging Pattern9. The Declarative Living and Tag Gardening Pattern10. The Semantic Web Grounding Pattern11. The Persistent Rights Management (PRM) Pattern12. The Structured Information Pattern
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References
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This lecture has been based on material from :
• James Governor, Dion Hinchcliffe, Duane Nickull, “Web 2.0 Architectures”, O'Reilly Media May 2009O Reilly Media, May 2009.
http://oreilly.com/catalog/9780596514433
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