last updated 03-12-2020
A resource node holds the descriptive metadata for content, as well as grouping together an original file and all of the derivatives files generated from it.
The model for exactly what constitutes an object in Islandora 8 is flexible and can be adapted to the needs of specific users. For example, the Islandora Defaults configuration considers an object as a resource node of the type "Repository Item" which contains descriptive metadata about the object. Attached to that Node are one or more Media, each representing a file that is part of this object, such as "Original File", "Thumbnail", "Preservation Master", etc. With this model, every original file uploaded into Islandora has its own resource node.
Multi-file Media configurations also attach Media to a parent node, but allow for that node to be represened by multiple "Original File"s. In this model, a Media contains the original file as well as any derivative files created from it (thumbnail, service file, etc.).
For an example of where these two different approaches could apply, the basic configuration might make sense for a book that has rich page-level metadata, so that each page would be its own Node with its own metadata record; the multi-file media configuration might be a better fit for a book that does not have page-level metadata (except an ordering or page numbers), so that each Media would represent one page, and all pages (Media) would be attached to a single parent Node/metadata record for the entire book.
As we learned in the introduction, objects in an Islandora repository are represented as a combination of resource nodes, media, and files in Drupal. Because of this, their metadata profile, display, form (and much more) are configurable through the Drupal UI. This gives repository administrators a huge degree of control over their repository without any need for coding. Much more so than ever before. And since we're using a core Drupal solution for modeling our resource nodes and media, compatibility with third-party modules is virtually guaranteed. This opens up a plethora of solutions from the Drupal community that will save you untold time and effort when implementing your repository with Islandora.
Resource nodes have some basic properties that are common to all nodes, regardless of its content type. These properties are not fields. This means that they cannot be removed and have limited configurability. Their name, what type of data they hold, etc... are all baked in. Here's an example of the basic properties on nodes:
nid: 1 uid: 1 title: "I am an Islandora 8 object" created: 1550703004 changed: 1550703512 uuid: 02932f2c-e4c2-4b7e-95e1-4aceab78c638 type: islandora_object status: 1
As you can see, it's all system data used at the Drupal level to track the basics.
|nid||The local ID for the node|
|uuid||The global ID for any entity|
|title||The title for the node|
|created||Timestamp of when the node was created|
|changed||Timestamp of when the node was last updated|
|type||Content type (e.g. which group of fields are present on the node)|
|status||Published, unpublished, etc...|
Compared to Islandora 7
These node properties directly correspond to following Islandora 7.x object properties:
|Islandora 7||Islandora 8|
The small amount of configurability available for these properties is found on the content type editing form where a user can choose to change the label of the title field, whether or not to display author information on the node's page, etcetera. These settings will only apply to nodes of that particular content type.
To view all of a node's property and field values administrators can use the 'Devel' tab's 'Load' section:
In addition to the basic node properties identified above, resource nodes (like all Drupal nodes) can have fields. Most of what we would think of as descriptive metadata is stored as fields. Resource nodes use 'content types' to define a specific set of required and optional fields it has; we can think of content types as metadata profiles for our objects. For example, you might have a content type for a set of repository objects that have very specialized metadata requirements but another content type for generic repository objects that share a more general set of metadata fields. A resource node's content type is set on its creation and is immutable. The section on metadata describes in more detail how fields on Islandora objects work.
Islandora has a notion of a content model, which is used to identify what type of content is being represented by a node (e.g. an image, a video, a collection of other items, etc...). This is done using a special field, Model, which accepts taxonomy terms from the Islandora Models vocabulary. By applying a term from the Islandora Models vocabulary to a node, Islandora will become aware of how to handle the node in response to certain events, like choosing a viewer or generating derivatives.
Compared to Islandora 7
Content models in Islandora 7 were immutable and contained restrictions as to what types of datastreams could be associated with an object. Islandora 8 imposes no such restrictions. Content models can be changed at any time, and they in no way dictate what types of media can be associated with a node.
All resource nodes can be linked to any number of media. The media associated with a resource node can be managed using the "Media" tab when viewing a node. Much like the "Members" tab, Actions can be performed in bulk using the checkboxes and Actions dropdown.
See the media section for more details.
Drupal uses "display modes" (also called "view modes") as alternative ways to present content to users. You may be familiar with the "full" and "teaser" versions of nodes, which are rendered using two corresponding display modes. Islandora makes use of display modes to control how media content is displayed. Islandora Defaults provides two display modes for Media, one which renders the OpenSeadragon viewer and the other which renders the pdf.js viewer. These two display modes can be enabled by using "Display hints" in the node edit form, or you can configure Islandora to use a specific display mode for all media based on the file's Mime type. Both methods make use of Contexts.
To set the display mode on the resource node's edit form, select the display mode you want to use for that node in the Display hints field:
Due to the associated Context configurations ("Open Seadragon" and "PDFjs Viewer") that are shipped with Islandora Defaults, the selected display mode will then be used when the resource node's page is rendered.
At a global level, there are a couple of ways to tell Drupal to use the PDFjs viewer to render the content of the media field whenever the media has a Mime type of
The first way is to edit the "PDFjs Viewer" Context. By default, this Context tells Drupal to use the PDFjs viewer if the node has the term "PDFjs" (yes, that's a taxonomy term):
If you add the Condition "Node has Media with Mime type" and configure it to use
application/pdf as the Mime type, like this:
Context will use whichever Condition applies (as long as you don't check "Require all conditions"). That is, if the "PDFjs" display hint option in the node edit form is checked, or if the node's media has a Mime type of
application/pdf, the media content will be rendered using the PDFjs viewer.
The second way to use the media's Mime type to render its content with the PDFjs viewer is to create a separate Context that will detect the media's Mime type and use the configured display mode automatically. To do this, create a new Context. Add a "Node has Media with Mime type" condition and specify the Mime type, and then add a "Change View mode" Reaction that selects the desired display mode:
Finally, save your Context. From that point on, whenever the media for a node has the configured Mime type, Drupal will render the media using the corresponding display mode.
The node-level and global approaches are not exclusive to one another. One Context can override another depending on the order of execution. Whichever Condition applies last between the node-level Condition (which in this case is the "Node has term" condition) the global Condition (which is "Node has Media with Mime type"), that one will override the other. An example of having the display mode specified in the node edit form intentionally override the display mode based on Mime type is to have media with the
image/jp2 mime-type configured to use to use the OpenSeadragon viewer, but to manually select the OpenSeadragon display mode for nodes with JPEG media (for example, a very large JPEG image of a map, where the OpenSeadragon's pan and zoom features would be useful).
Islandora has a notion of membership, which is used to create a parent/child relationship between
two resource nodes. Membership is denoted using another special field, "Member Of".
The "Member Of" field can hold multiple references, so it is possible for a single child to belong to multiple parents, but may also complicate the creation of breadcrumbs. Any two nodes can be related in this way, though typically, the parent node has a content model of Collection or Paged Content (see their respective pages for more details).
Compared to Islandora 7
In Islandora 7, there was a distinction between belonging to a collection and belonging to a compound object. In Islandora 8, this distinction is not present, essentially allowing every resource node to be part of a compound object.
Child v. Member
Islandora 8 uses the "child" and "member" descriptor for resource nodes that store a reference to another resource node in the "Member Of" field interchangeably. Administrators will more often see the "member" terminology more often while front-end users will usually see "child" terminology.
For any node, its Children tab can be used to see all its members. You can also perform Actions in bulk on members using the checkboxes and the Actions dropdown as well as clicking on the Re-order Children tab to adjust the order in which they display.