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Figure 1 – Fedora repository as Mediator for Services and Content
Figure 2 – Fedora Administrator Login Screen
Figure 3 – New Object Dialog
Figure 4 – Configuring an Object
Figure 5 – Datastream Display
Figure 6 – Adding a New Managed Content Datastream
Figure 7 – Complete Datastreams for Example 1
Figure 8 – Example 1 Fedora Digital Object and Datastreams
Figure 9 – Adding a Datastream with Type Redirect
Figure 10 – Example 2 Datastream Display
Figure 11 – Example Fedora Digital Object and Redirected Datastream
Figure 12 – Abstract View: Key Fedora Components for Producing Disseminations of Content
Figure 13 – Relationships Between Data objects and CModel/SDef/SDep Objects for CMA
Figure 14 – Dynamic Dissemination Access
Figure 15 – Example 3 Linking a Fedora Digital Object to a Content Model
Figure 16 – Example 3 Dissemination via CMA
Figure 17 – Dissemination with Redirect Datastream

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1. It supports the creation and management of digital content objects (from this point on called digital objects Fedora Digital Objects or FDO) that can aggregate data from multiple sources. For example, a digital object an FDO might be a set of TIFF images that are the individual page images of a scanned document. The data sources may be either locally managed within the Fedora software or sourced from another URL accessible network server. The data sources may be content or metadata. You may think of these digital objects FDOs as advanced digital documents, especially in light of the feature described next.
   
   
2. It supports the association of web services with the digital objects FDOs. These services typically consume the data packaged within the digital object FDOs to produce dynamic disseminations from the digital objectthem. For example, the digital object FDO described above with multiple TIFF page images may be associated with a service that OCRs the images that are components of the digital object FDO and disseminates an HTML version of the pages. The services may be either local to the machine of the respective Fedora server or sourced from another network accessible server that is addressable via a URL. In this manner, Fedora acts as a mediation layer that coordinates local and distributed data and web services within a uniform framework. This is illustrated in Figure 1.
   
   
3. It provides uniform access web-based interfaces to these digital objects FDOs, through REST requests and more powerful SOAP-based methods. These interfaces consist of a set of built-in methods to access characteristics common to all digital objects FDOs such as key metadata and internal structure. These include a method to introspect on an object to reveal the set of methods that constitute the extended behavior of that object. For example, a client could use these built-in methods to "learn" about the capability of the digital object FDO described above to dynamically disseminate an HTML page from a set of TIFF images.
   The benefits of these are two-fold:
   
   
   1. Clients accessing Fedora digital objects Digital Objects can rely on uniform access regardless of the nature of the object.
      
      
   2. The disseminations available from an object are independent of the internal structure of the object. For example, the client interface of the example above in which HTML is disseminated from a set of source TIFF pages could remain constant regardless of whether the underlying object contained TIFF images, JPEG, PDF, or even simple static HTML. This gives the content developer great freedom to modify a repository's internals without disrupting the client and user views of the content.
      
      
4. It presents a uniform and powerful REST and SOAP-based management interface. All internal operations of the repository such as object creation and management are available through these APIs, providing the hooks for integrating Fedora into a variety of environments. These makes Fedora useful as the foundation for advanced content management applications.
   
   
5. It includes a comprehensive versioning framework that tracks the evolution of objects and provides access to earlier versions.
   
   
6. It includes a basic relationship framework for representing the links among digital objects FDOs.
   
   
7. It supports ingest and export of digital objects FDOs in a variety of XML formats. This enables interchange between Fedora and other XML-based applications and facilitates archiving tasks.

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1. Fedora Digital Object or FDO – This is the basic unit for information aggregation in Fedora. At a minimum a digital object an FDO has:
   
   
   1. A Persistent Identifier or PID – The PID provides the key by which the digital object FDO is accessed from the repository.
      
      
   2. Dublin Core – It provides a basic description of the digital object FDO.
      
      
2. Datastream – A component of a digital object an FDO that represents a data source. A digital object An FDO may have just the basic Dublin Core Datastream, or any number of additional Datastreams. Each Datastream can be any MIME-typed data or metadata, and can either be content managed locally in the Fedora repository or by some external data source (and referenced by a URL). When you create a new Datastream in a digital objectan FDO, you assign it to one of four types, or control groups, depending on the nature of the data that it represents.
   
   
   1. Managed Content (M): Datastream content is stored and managed within the Fedora repository's persistent storage. The content can be any MIME type including XML.
      
      
   2. Inline XML (X): A special case of M, restricted to well-formed XML. In this case, the Datastream content is stored as part of the XML structure of the digital object FDO itself and is thus included when the digital object it is exported (e.g., for archival purposes).
      
      
   3. Externally Referenced (E): Datastream content is external to the Fedora repository and is referenced by a URL that is recorded within the digital object FDO. The content can be any MIME type including XML.
      
      
   4. Redirected Content (R): Like E, but Datastream content is delivered to the client without any mediation by Fedora; i.e., via an HTTP redirect. You should use this Datastream type when the external content is a web page with relative links or it is streaming audio or video. The content can be any MIME type including XML.

Decisions about what to include in a digital object an FDO and how to configure its Datastreams are basic modeling choices as you develop your repository. The examples in this tutorial demonstrate some common models that you may find useful as you develop your application.

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It is often useful to provide access to a digital document in several formats. For example an ePrints server might provide HTML for those who wish to render the document in a browser, PDF for those who wish to view the document with author-determined formatting, and TeX for those who wish to access and use the document source. This example demonstrates how to construct a digital object an FDO where each Datastream corresponds to an available format. More advanced techniques, demonstrated later in this tutorial, make it possible to achieve the same results by generating formats dynamically from a single base format. But for now, we'll stick to simple static aggregation.

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1. You will notice that the Control Group of the DC Datastream is Internal XML Metadata. As explained earlier, Fedora has a number of control group types, of which this is one. This type is appropriate for metadata that is represented in XML – Dublin Core metadata being one example. A digital object An FDO can have multiple metadata Datastreams, for example MARC, LOM, Dublin Core, and others.
   
2. You can directly edit the Dublin Core metadata – e.g., add new Dublin Core fields – by selecting the Edit button and modifying the contents of the text pane. When you press Save Changes..., Fedora will check that the Datastream is well-formed XML.

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You will notice as you click through each Datastream that there is a Fedora URL, giving the unique URL to access each Datastream from the Fedora repository. Try going to a browser and entering one of these URLs – the browser will download the Datastream and display it. These URLs can be used by web applications and REST-based web services that access Datastreams from Fedora digital objectsDigital Objects. Note that if you are building SOAP-based web services, there are also SOAP methods (getDataStream and getDatastreamDissemination) that provide Datastream access. You can also try entering the root URL for the entire digital object FDO, which is simply the common prefix of all the Datastream URLs – e.g., http://localhost:8080/fedora/get/demo:100. This accesses the header page for the digital object FDO, which allows you to access its Datastreams (available through the item index hyperlink) and disseminations (available through the dissemination index hyperlink).

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*Figure 8 -- Example 1 Fedora Digital Object and Datastreams*
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