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The following sections describe the various functional aspects of the DSpace system.

System Design

Data Model

Data Model Diagram

The way data is organized in DSpace is intended to reflect the structure of the organization using the DSpace system. Each DSpace site is divided into communities, which can be further divided into sub-communities reflecting the typical university structure of college, department, research center, or laboratory.

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Plugin Manager

The PluginManager is a very simple component container. It creates and organizes components (plugins), and helps select a plugin in the cases where there are many possible choices. It also gives some limited control over the lifecycle of a plugin.

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The mediafilter is a simple example of a plugin implementation. Refer to the Business Logic Layer for more details on Plugins.

Metadata

Broadly speaking, DSpace holds three sorts of metadata about archived content:

• Descriptive Metadata: DSpace can support multiple flat metadata schemas for describing an item. A qualified Dublin Core metadata schema loosely based on the Library Application Profile set of elements and qualifiers is provided by default. The set of elements and qualifiers used by MIT Libraries comes pre-configured with the DSpace source code. However, you can configure multiple schemas and select metadata fields from a mix of configured schemas to describe your items. Other descriptive metadata about items (e.g. metadata described in a hierarchical schema) may be held in serialized bitstreams. Communities and collections have some simple descriptive metadata (a name, and some descriptive prose), held in the DBMS.
• Administrative Metadata: This includes preservation metadata, provenance and authorization policy data. Most of this is held within DSpace's relational DBMS schema. Provenance metadata (prose) is stored in Dublin Core records. Additionally, some other administrative metadata (for example, bitstream byte sizes and MIME types) is replicated in Dublin Core records so that it is easily accessible outside of DSpace.
• Structural Metadata: This includes information about how to present an item, or bitstreams within an item, to an end-user, and the relationships between constituent parts of the item. As an example, consider a thesis consisting of a number of TIFF images, each depicting a single page of the thesis. Structural metadata would include the fact that each image is a single page, and the ordering of the TIFF images/pages. Structural metadata in DSpace is currently fairly basic; within an item, bitstreams can be arranged into separate bundles as described above. A bundle may also optionally have a primary bitstream. This is currently used by the HTML support to indicate which bitstream in the bundle is the first HTML file to send to a browser. In addition to some basic technical metadata, a bitstream also has a 'sequence ID' that uniquely identifies it within an item. This is used to produce a 'persistent' bitstream identifier for each bitstream. Additional structural metadata can be stored in serialized bitstreams, but DSpace does not currently understand this natively.

Packager Plugins

Packagers are software modules that translate between DSpace Item objects and a self-contained external representation, or "package". A Package Ingester interprets, or ingests, the package and creates an Item. A Package Disseminator writes out the contents of an Item in the package format.

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More information about calling Packagers to ingest or disseminate content can be found in the Package Importer and Exporter section of the System Administration documentation.

Crosswalk Plugins

Crosswalks are software modules that translate between DSpace object metadata and a specific external representation. An Ingestion Crosswalk interprets the external format and crosswalks it to DSpace's internal data structure, while a Dissemination Crosswalk does the opposite.

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The Packager plugins and OAH-PMH server make use of crosswalk plugins.

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User Management

Although many of DSpace's functions such as document discovery and retrieval can be used anonymously, some features (and perhaps some documents) are only available to certain "privileged" users. E-People and Groups are the way DSpace identifies application users for the purpose of granting privileges. This identity is bound to a session of a DSpace application such as the Web UI or one of the command-line batch programs. Both E-People and Groups are granted privileges by the authorization system described below.

User Accounts (E-Person)

DSpace holds the following information about each e-person:

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Administrators can also use groups as "roles" to manage the granting of privileges more efficiently.

Access Control

Authentication

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Authentication Authentication

Authentication is when an application session positively identifies itself as belonging to an E-Person and/or Group. In DSpace 1.4 and later, it is implemented by a mechanism called Stackable Authentication: the DSpace configuration declares a "stack" of authentication methods. An application (like the Web UI) calls on the Authentication Manager, which tries each of these methods in turn to identify the E-Person to which the session belongs, as well as any extra Groups. The E-Person authentication methods are tried in turn until one succeeds. Every authenticator in the stack is given a chance to assign extra Groups. This mechanism offers the following advantages:

• Separates authentication from the Web user interface so the same authentication methods are used for other applications such as non-interactive Web Services
• Improved modularity: The authentication methods are all independent of each other. Custom authentication methods can be "stacked" on top of the default DSpace username/password method.
• Cleaner support for "implicit" authentication where username is found in the environment of a Web request, e.g. in an X.509 client certificate.

Authorization

DSpace's authorization system is based on associating actions with objects and the lists of EPeople who can perform them. The associations are called Resource Policies, and the lists of EPeople are called Groups. There are two built-in groups: 'Administrators', who can do anything in a site, and 'Anonymous', which is a list that contains all users. Assigning a policy for an action on an object to anonymous means giving everyone permission to do that action. (For example, most objects in DSpace sites have a policy of 'anonymous' READ.) Permissions must be explicit - lack of an explicit permission results in the default policy of 'deny'. Permissions also do not 'commute'; for example, if an e-person has READ permission on an item, they might not necessarily have READ permission on the bundles and bitstreams in that item. Currently Collections, Communities and Items are discoverable in the browse and search systems regardless of READ authorization.

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Policies can apply to individual e-people or groups of e-people.

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Getting content into DSpace

The Manual DSpace Submission and Workflow System

Rather than being a single subsystem, ingesting is a process that spans several. Below is a simple illustration of the current ingesting process in DSpace.

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• Assigns an accession date
• Adds a "date.available" value to the Dublin Core metadata record of the item
• Adds an issue date if none already present
• Adds a provenance message (including bitstream checksums)
• Assigns a Handle persistent identifier
• Adds the item to the target collection, and adds appropriate authorization policies
• Adds the new item to the search and browse index

Workflow Steps

A collection's workflow can have up to three steps. Each collection may have an associated e-person group for performing each step; if no group is associated with a certain step, that step is skipped. If a collection has no e-person groups associated with any step, submissions to that collection are installed straight into the main archive.

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Submission Workflow in DSpace

If a submission is rejected, the reason (entered by the workflow participant) is e-mailed to the submitter, and it is returned to the submitter's 'My DSpace' page. The submitter can then make any necessary modifications and re-submit, whereupon the process starts again.

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The reason for this apparently arbitrary design is that is was the simplest case that covered the needs of the early adopter communities at MIT. The functionality of the workflow system will no doubt be extended in the future.

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Import and

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Export

DSpace includes batch tools to import and export items in a simple directory structure, where the Dublin Core metadata is stored in an XML file. This may be used as the basis for moving content between DSpace and other systems. For more information see Item Importer and Exporter.

DSpace also includes various package importer and exporter tools, which support many common content packaging formats like METS. For more information see Package Importer and Exporter.

Supervision and Collaboration

In order to facilitate, as a primary objective, the opportunity for thesis authors to be supervised in the preparation of their e-theses, a In order to facilitate, as a primary objective, the opportunity for thesis authors to be supervised in the preparation of their e-theses, a supervision order system exists to bind groups of other users (thesis supervisors) to an item in someone's pre-submission workspace. The bound group can have system policies associated with it that allow different levels of interaction with the student's item; a small set of default policy groups are provided:

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This functionality could also be used in situations where researchers wish to collaborate on a particular submission, although there is no particular collaborative workspace functionality.

Persistent URLs and Identifiers 

Handles

Researchers require a stable point of reference for their works. The simple evolution from sharing of citations to emailing of URLs broke when Web users learned that sites can disappear or be reconfigured without notice, and that their bookmark files containing critical links to research results couldn't be trusted in the long term. To help solve this problem, a core DSpace feature is the creation of a persistent identifier for every item, collection and community stored in DSpace. To persist identifiers, DSpace requires a storage- and location- independent mechanism for creating and maintaining identifiers. DSpace uses the CNRI Handle System for creating these identifiers. The rest of this section assumes a basic familiarity with the Handle system.

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Handles can be written in two forms:

hdl:1721.123/4567
http://hdl.handle.net/1721.123/4567

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It is important to note that DSpace uses the CNRI Handle infrastructure only at the 'site' level. For example, in the above example, the DSpace site has been assigned the prefix '1721.123'. It is still the responsibility of the DSpace site to maintain the association between a full Handle (including the '4567' local part) and the community, collection or item in question.

Bitstream 'Persistent' Identifiers

Similar to handles for DSpace items, bitstreams also have 'Persistent' identifiers. They are more volatile than Handles, since if the content is moved to a different server or organization, they will no longer work (hence the quotes around 'persistent'). However, they are more easily persisted than the simple URLs based on database primary key previously used. This means that external systems can more reliably refer to specific bitstreams stored in a DSpace instance.

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dspace url/bitstream/handle/sequence ID/filename

For example:

https://dspace.myu.edu/bitstream/123.456/789/24/foo.html

The above refers to the bitstream with sequence ID 24 in the item with the Handle hdl:123.456/789. The foo.html is really just there as a hint to browsers: Although DSpace will provide the appropriate MIME type, some browsers only function correctly if the file has an expected extension.

Storage Resource Broker (SRB) Support

DSpace offers two means for storing bitstreams. The first is in the file system on the server. The second is using SRB (Storage Resource Broker). Both are achieved using a simple, lightweight API.

SRB is purely an option but may be used in lieu of the server's file system or in addition to the file system. Without going into a full description, SRB is a very robust, sophisticated storage manager that offers essentially unlimited storage and straightforward means to replicate (in simple terms, backup) the content on other local or remote storage resources.

Search and Browse

DSpace allows end-users to discover content in a number of ways, including:

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Another important mechanism for discovery in DSpace is the browse. This is the process whereby the user views a particular index, such as the title index, and navigates around it in search of interesting items. The browse subsystem provides a simple API for achieving this by allowing a caller to specify an index, and a subsection of that index. The browse subsystem then discloses the portion of the index of interest. Indices that may be browsed are item title, item issue date, item author, and subject terms. Additionally, the browse can be limited to items within a particular collection or community.

HTML Support

For the most part, at present DSpace simply supports uploading and downloading of bitstreams as-is. This is fine for the majority of commonly-used file formats – for example PDFs, Microsoft Word documents, spreadsheets and so forth. HTML documents (Web sites and Web pages) are far more complicated, and this has important ramifications when it comes to digital preservation:

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• No dynamic content (CGI scripts and so forth)
• All links to preserved content must be relative links, that do not refer to 'parents' above the 'root' of the HTML document/site:
  • diagram.gif is OK
  • image/foo.gif is OK
  • ../index.html is only OK in a file that is at least a directory deep in the HTML document/site hierarchy
  • /stylesheet.css is not OK (the link will break)
  • http://somedomain.com/content.html is not OK (the link will continue to link to the external site which may change or disappear)
• Any 'absolute links' (e.g. http://somedomain.com/content.html) are stored 'as is', and will continue to link to the external content (as opposed to relative links, which will link to the copy of the content stored in DSpace.) Thus, over time, the content referred to by the absolute link may change or disappear.

OAI Support

The Open Archives Initiative has developed a protocol for metadata harvesting. This allows sites to programmatically retrieve or 'harvest' the metadata from several sources, and offer services using that metadata, such as indexing or linking services. Such a service could allow users to access information from a large number of sites from one place.

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DSpace's OAI service does support the exposing of deletion information for withdrawn items, but not for items that are 'expunged' (see above). DSpace also supports OAI-PMH resumption tokens.

SWORD Support

SWORD (Simple Web-service Offering Repository Deposit) is a protocol that allows the remote deposit of items into repositories. SWORD was further developed in SWORD version 2 to add the ability to retrieve, update, or delete deposits. DSpace supports the SWORD protocol via the 'sword' web application and SWord v2 via the swordv2 web application. The specification and further information can be found at http://swordapp.org.

OpenURL Support

DSpace supports the OpenURL protocol from SFX, in a rather simple fashion. If your institution has an SFX server, DSpace will display an OpenURL link on every item page, automatically using the Dublin Core metadata. Additionally, DSpace can respond to incoming OpenURLs. Presently it simply passes the information in the OpenURL to the search subsystem. A list of results is then displayed, which usually gives the relevant item (if it is in DSpace) at the top of the list.

Creative Commons Support

DSpace provides support for Creative Commons licenses to be attached to items in the repository. They represent an alternative to traditional copyright. To learn more about Creative Commons, visit their website. Support for license selection is controlled by a site-wide configuration option, and since license selection involves interaction with the Creative Commons website, additional parameters may be configured to work with a proxy server. If the option is enabled, users may select a Creative Commons license during the submission process, or elect to skip Creative Commons licensing. If a selection is made, metadata and (optionally) a copy of the license text is stored along with the item in the repository. There is also an indication - text and a Creative Commons icon - in the item display page of the web user interface when an item is licensed under Creative Commons. For specifics of how to configure and use Creative Commons licenses, see the configuration section.

Subscriptions

As noted above, end-users (e-people) may 'subscribe' to collections in order to be alerted when new items appear in those collections. Each day, end-users who are subscribed to one or more collections will receive an e-mail giving brief details of all new items that appeared in any of those collections the previous day. If no new items appeared in any of the subscribed collections, no e-mail is sent. Users can unsubscribe themselves at any time. RSS feeds of new items are also available for collections and communities.

Import and Export

DSpace includes batch tools to import and export items in a simple directory structure, where the Dublin Core metadata is stored in an XML file. This may be used as the basis for moving content between DSpace and other systems. For more information see Item Importer and Exporter.

DSpace also includes various package importer and exporter tools, which support many common content packaging formats like METS. For more information see Package Importer and Exporter.

Registration

Registration is an alternate means of incorporating items, their metadata, and their bitstreams into DSpace by taking advantage of the bitstreams already being in accessible computer storage. An example might be that there is a repository for existing digital assets. Rather than using the normal interactive ingest process or the batch import to furnish DSpace the metadata and to upload bitstreams, registration provides DSpace the metadata and the location of the bitstreams. DSpace uses a variation of the import tool to accomplish registration.

Statistics

DSpace offers system statistics for administrator usage, as well as usage statistics on the level of items, communities and collections.

System Statistics

Various statistical reports about the contents and use of your system can be automatically generated by the system. These are generated by analyzing DSpace's log files. Statistics can be broken down monthly.

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• A customizable general overview of activities in the archive, by default including:
  • Number of items archived
  • Number of bitstream views
  • Number of item page views
  • Number of collection page views
  • Number of community page views
  • Number of user logins
  • Number of searches performed
  • Number of license rejections
  • Number of OAI Requests
• Customizable summary of archive contents
• Broken-down list of item viewings
• A full break-down of all performed actions
• User logins
• Most popular searches
• Log Level Information
• Processing information!stats_genrl_overview.png!
  The results of statistical analysis can be presented on a by-month and an in-total report, and are available via the user interface. The reports can also either be made public or restricted to administrator access only.

Item, Collection and Community Usage Statistics

Usage statistics can be retrieved from individual item, collection and community pages. These Usage Statistics pages show:

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*File Downloads information is only displayed for item-level statistics. Note that downloads from separate bitstreams are also recorded and represented separately. DSpace is able to capture and store File Download information, even when the bitstream was downloaded from a direct link on an external website.

Checksum Checker

The purpose of the checker is to verify that the content in a DSpace repository has not become corrupted or been tampered with. The functionality can be invoked on an ad-hoc basis from the command line, or configured via cron or similar. Options exist to support large repositories that cannot be entirely checked in one run of the tool. The tool is extensible to new reporting and checking priority approaches.

Usage Instrumentation

DSpace can report usage events, such as bitstream downloads, to a pluggable event processor. This can be used for developing customized usage statistics, for example. Sample event processor plugins writes event records to a file as tab-separated values or XML.

Choice Management and Authority Control

This is a configurable framework that lets you define plug-in classes to control the choice of values for a given DSpace metadata fields. It also lets you configure fields to include "authority" values along with the textual metadata value. The choice-control system includes a user interface in both the Configurable Submission UI and the Admin UI (edit Item pages) that assists the user in choosing metadata values.

Introduction and Motivation

Definitions

Choice Management

This is a mechanism that generates a list of choices for a value to be entered in a given metadata field. Depending on your implementation, the exact choice list might be determined by a proposed value or query, or it could be a fixed list that is the same for every query. It may also be closed (limited to choices produced internally) or open, allowing the user-supplied query to be included as a choice.

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This works in addition to choice management to supply an authority key along with the chosen value, which is also assigned to the Item's metadata field entry. Any authority-controlled field is also inherently choice-controlled.

About Authority Control

The advantages we seek from an authority controlled metadata field are:

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1. Authorities are external to DSpace. The source of authority control is typically an external database or network resource.
   • Plug-in architecture makes it easy to integrate new authorities without modifying any core code.
2. This authority proposal impacts all phases of metadata management.
   • The keyword vocabularies are only for the submission UI.
   • Authority control is asserted everywhere metadata values are changed, including unattended/batch submission, LNI and SWORD package submission, and the administrative UI.

Some Terminology