Digitalcollections Model

Java library containing Domain Object classes of the Digital Collection's and Digital Humanities ecosystem. Primarily started from the needs for GLAMs (Galleries, Libraries, Archives, Museums) but not restricted to it.

Business Domain Model

The domain model follows the FRBR (Functional Requirements for Bibliographic Records). The model is not restricted to books but can handle all sort of creative works and their digital counterparts ("digital objects").

One core statement (taken from Music Cataloging at Yale) is:

"A work is realized by an expression, which is embodied in a manifestation, which is exemplified by an item."

And the central object of interest of digital collections is the DigitalObject as the digital representation of an item and curated Collections as group of digital objects.

• For presenting digital collections online the library offers Website and Webpage classes.
• For arranging and describing digital objects by topics the library offers Topic and Subtopic classes.
• For editorial contribution in the context of digital collections the library offers Article with rich text formatting and embedding of different media.

The following classes can be assigned to objects (where appropriate):

• a freely definable License
• a list of freely definable Identifiers, each of them identifying the object uniquely in an external source system, e.g. GND-ID ("gnd:104330171") or VIAF-ID ("viaf:96994450").

Class Diagram

The classes are modelled after the business domain model. Common properties and characteristics are expressed through some inheritance (Entity, Identifiable).

Technical Model Classes

This library supports practical handling of above domain model by adding paging, filtering and sorting classes.

Filtering-Model

Model for passing technology independent filter criterias

• from frontend to backend via URL-params,
• from Java code to backend

Backend has to take care about implementing technology dependent filtering for given criterias.

Filtering by using (user given) URL params

Example usage in a Spring MVC controller: return only webpages with active publication time range

Example URL: http://localhost/v5/webpages?publicationStart=gte:2021-01-01&publicationEnd=lt:2021-10-01

@Operation(summary = "Get all webpages")
@GetMapping(value = {"/v5/webpages", "/v2/webpages"}, produces = MediaType.APPLICATION_JSON_VALUE)
public PageResponse<Webpage> findAll(
    @RequestParam(name = "pageNumber", required = false, defaultValue = "0") int pageNumber,
    @RequestParam(name = "pageSize", required = false, defaultValue = "25") int pageSize,
    @RequestParam(name = "sortBy", required = false) List<Order> sortBy,
    @RequestParam(name = "publicationStart", required = false) FilterCriterion<LocalDate> publicationStart,
    @RequestParam(name = "publicationEnd", required = false) FilterCriterion<LocalDate> publicationEnd) {
  PageRequest pageRequest = new PageRequest(pageNumber, pageSize);
  ...
  Filtering filtering =
      Filtering.defaultBuilder()
          .add("publicationStart", publicationStart)
          .add("publicationEnd", publicationEnd)
          .build();
  pageRequest.setFiltering(filtering);
  return webpageService.find(pageRequest);
}

REST-API design for filtering was inspired by:

• REST API Design: Filtering, Sorting, and Pagination
• An example application using Spring boot MVC, Spring Data JPA with the ability to do filter, pagination and sorting.

Supported URL-params based filter operations

Mapping operation abbreviation to filter operation

Symbol	Operation	Example filter query param
eq	equals	filter=city:eq:Munich
eq_notset	equals or not set	filter=city:eq_notset:Munich
neq	not equals	filter=country:neq:de
gt	greater than	filter=amount:gt:10000
gt_notset	greater than or not set	filter=presentationEnd:gt_notset:2020-10-06
gte	greater than or equals	filter=amount:gte:10000
gte_notset	greater than or equals or not set	filter=amount:gte_notset:10000
lt	less than	filter=amount:lt:10000
lt_notset	less than or not set	filter=amount:lt_notset:10000
lt_set	less than and set	filter=amount:lt_set:10000
lte	less than or equals to	filter=amount:lte:10000
lte_set	less than or equals and set	filter=presentationStart:lte_set:2020-10-06
lte_notset	less than or equals or not set	filter=presentationStart:lte_notset:2020-10-06
in	in	filter=country:in:uk,usa,au
nin	not in	filter=country:nin:fr,de,nz
btn	between (inclusive)	filter=joiningDate:btn:2018-01-01,2016-01-01
like	like	filter=firstName:like:John
stw	starts with	filter=firstName:stw:A
set	value exists (not null)	filter=firstName:set:
notset	value is not set (null)	filter=firstName:notset:

Model-Serializing

Comes with a separate module for supporting serializing model objects to JSON (dc-model-jackson module) using Jackson

Builder

Many model objects already provide a builder method, which help to instantiate and fill model objects in a fluent way.

The builder internally holds all attributes of the model class and provides several methods to set or modify them.

By calling the build() method, the model object is instantiated, filled and returned.

Implementing builders

To implement a new builder, it is important to know, how they work internally. Since Lombok is used, every model class must be annotated with @SuperBuilder(buildMethodName = "prebuild"), to enable multi-tier inheritance.

As next step, you have to customize the builder by inheriting it from the upper-tier builder, e.g.:

public abstract static class Tier2Builder<C extends Tier2Object, B extends Tier2Builder<C, B>> 
    extends Tier1Builder<C, B> {
  
}

The prebuild configuration allows manipulation of the auto-generated build method, which is renamed to prebuild, so that you can write your own build method, which must at least execute prebuild.

Since Lombok ignores all member variable pre-settings of the classes (e.g. initializing a list member to an empty Array on instantiation), and internally holds a copy of all instance variables, an init() method to initialize the variables where neccessary was applied, which is executed by the constructor and by the build method. Please note, that you can execute init only after prebuild, since only prebuild gives you the instance of your model object.

As a reference, your build method, should minimally look like this:

public C build() {
  C c = prebuild();
  c.init();
  return c;
}

Systems using this library

• cudami (cultural digital asset management)