Data Storage in the Live Framework

There are several ways to associate data with a DataEntry in the Live Framework:

• Attribute Extension
• Element Extension
• Media Resource
• User Data
• Syndication Link
• Summary

This post is based on this thread on the MSDN forums.

Attribute Extension

Attribute extensions are a feature of the Feed Sync specification that can be used to add a user-defined attribute to any element in the Atom feed. The following is an example fragment of an Atom feed when an attribute extension added to a data entry:

<entry bird="Emu">

In this example, the added attribute is named bird and its value is Emu.

Attribute extensions are accessed through the AttributeExtensions property of the Resource class:

public Dictionary<XmlQualifiedName,String> AttributeExtensions { get; }

The attribute extensions can be accessed using standard Dictionary methods on the AttributeExtensions property. Attribute extensions are fairly easy to use and appear useful for storing relatively small quantities of data.

Element Extension

Element extensions are a feature of the Feed Sync specification that can be used to add a user-defined element under any parent element on an Atom feed. The following is an example fragment of an Atom feed when an element extension has been added to a data entry:

<entry>
     …
     <Bird xmlns=http://schemas.datacontract.org/2004/07/NAMESPACE  xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
          <Flightless>true</Flightless> 
          <Species>Emu</Species> 
     </Bird>
</entry>

In this example, the entire Bird element (except the namespace definitions) is user-defined and can contain any valid XML.

Element extensions are accessed through the ElementExtensions property of the Resource class:

public List<ResourceMarkupExtension> ElementExtensions { get; }

Simple data can be added as an element extension by creating a ResourceMarkupExtension object and using standard List methods on the ElementExtensions property. It is also possible to use Data Contract serialization to serialize and deserialize an object into an element extension. Element extensions are slightly harder to use than attribute extensions but allow for much richer form of structured content.

Media Resource

Media resources allow arbitrary data to be stored as a blob and associated with a data entry containing its metadata. Although referred to as media resources there is no restriction on the type of data contained in media resources.

Media resources are uploaded using the Add and AddAsync methods of the DataEntryCollection class, for example:

public DataEntry Add(Stream mediaResource, String slug);

where slug is a string used to identify the media resource on the feed. It could, for example, be the filename the stream is attached to.

Media resources are downloaded using the ReadMediaResource or ReadMediaResourceAsync methods of the DataEntry class, for example:

public void ReadMediaResource(Stream destination);

Media resources appear to be a powerful facility for associating large amounts of data to a feed. An obvious use, for example, is adding images to a feed as media resources.

User Data

User data can also be added directly to a data entry where it is serialized into user-data elements managed by the live operating environment. The Live Framework uses the JSON Data Contract serializer to serialize this data.

User data is accessed on a data entry using the GetUserEntry<T> and SetUserData<T> methods of the DataEntryResource class, namely:

public T GetUserData<T>();
public void SetUserData<T>(T userData);

where T is a serializable user-defined class.

User data seems to be pretty similar in form and function to element extensions.

Syndication Link

Syndication links can be used to associate other feeds with a data entry.

A syndication link is created using a SyndicationLink constructor such as:

public SyndicationLink( Uri uri, string relationshipType, string title, string mediaType, long length );

and associating this syndication link with the data entry through the following Resource property:

public List<SyndicationLink> Links { get; }

Syndication links appear trivial to use but also look pretty interesting for creating interesting webs of interleaved data.

Summary

Summary data simply refers to use of the Summary property of the data entry for storing text data.

The Summary property of the Resource class is defined as:

public string Summary { get; set; }

Summary data is utterly trivial to use and could be useful if the summary text essentially comprises the content of the data entry.

To Do

The usability statements above are fairly banal and would be much more helpful if I had put any kind of quantification regarding both queryability and performance. Hopefully, I will get round to that sooner or later.

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