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CGI ('Context-Guided-Ingest') is an attempt the remedy this problem, and improve ingest functionality generally, by providing a small set of service APIs and implementations that constitute more flexible and extensible equivalents to the content API wrappers. To ensure compatibility with previous work, as well as enhance general system modularity, CGI will be offered as a separate add-on or module and require no changes to the content API. Of course to utilize these services, new application code will have to be written. Over time, if CGI services prove useful, it may make sense to begin to abandon or deprecate the wrapper approach, but this will not be an immediate requirement of using CGI.

The Model

Concepts

To best describe the services, we will introduce a few terms with specific meaning in the domain model of CGI. First, an IngestContext (or merely context when contextually clear ) means a container of persistent state with a determinate life-cycle associated with a specific DSpace item. One could imagine other contexts (for Collections, etc), but since Items are the units of ingest, the range of the IngestContexts is restricted to them. An attribute is a simple name/value pair that belongs to the persistent state of the context. Generally, the life-cycle of an IngestContext begins whenever an API call asserting an attribute on a DSpace item occurs, and ends whenever the item is installed in the repository. The intent is that the context will live for the duration of the ingest, and then be discarded. This is very important to understand, that the IngestContext does not represent any kind of permanent 'extended item metadata' facility, although it can of course hold metadata for the item. Finally, an IngestResource (again, usually just resource), is an instance of any class that can be utilized to perform ingest functions (in UI, workflow, etc) that is not specific to an item. Examples of resources might be metadata templates, input forms, submission steps, curation task sets, etc. CGI places no restrictions on what could count as a resource.

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Combining these 2 services allows application code to select appropriate resources based on context attributes: thus have context help guide ingest.

Service APIs

To make the preceding descriptions a little more concrete, but also to illustrate how simple they might be, here are some prototype APIs.
NB: these are for illustrative purposes only, and are subject to change or outright abandonment.
ResourceMapService

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// set an attribute in the IngestContext for item
public void setAttribute(int itemId, String name, String value);

// get an attribute from the IngestContext for item
public void getAttribute(int itemId, String name);

// remove Ingest context
public void clear(int itemId);

// obtain the resource we need
public <T> T findResource(int itemId, Class<T> resClass);

Finding Resources

The observant reader will notice that the IngestService findResource method returns a resource (of a given type) for an item without any additional parameters or information. How is this possible? On what basis is the selection made? CGI assumes that, in general, each resource type bears a similar relationship with each of its items, and thus that it can be expressed in a rule or formula. For reasons that will become apparent, these rules are known as expressions in a grammar called RCL (Resource Composition Language). In most cases, RCL just amounts to a very simple template. For example, suppose we wanted to express the rule that DSpace currently uses in selecting an input form for configurable submission. We would write the property containing the expression as:

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It is the responsibility of the agent configuring RCL expressions to ensure that a default resource is always available, if this is the desired behavior; CGI will happily allow an expression to evaluate to null.

The Implementation

For clients of the CGI services, knowledge of the APIs and configuration properties discussed above should be sufficient to obtain the primary benefits of the facility: it makes no difference how they are implemented. But

Persistence