Let’s face it, RDF Graph datastores have not become the go-to database for application development like MySQL, MongoDB, and others have. Why? It is not that they cannot scale to handle the volume and velocity of data, nor the variety of structured and unstructured types.
Perhaps it is the lack of application development frameworks integrated with RDF. After all any application needs to not only store and query the data but provide users with the means to interact with that data, whether it be data entry forms, charts, graphs, visualizations and more.
However application development frameworks target popular back-ends accessible via JDBC and, now we are in the 21century, OData. RDF and SPARQL are not on their radar … that is unless we wrap RDF with OData so that the world of these application development environments is opened up to RDF Graph datastores.
OData2SPARQL provides that Janus-inflexion point, hiding the nuances of the RDF Graph behind an OData service which can then be consumed by powerful development environments such as OpenUI5 and WebIDE.
This article shows how an RDF Graph CRUD application can be rapidly developed, yet without losing the flexibility that HTML5/JavaScript offers, from which it can be concluded that there is no reason preventing the use of RDF Graphs as the backend for production-capable applications.
A video of this demo can be found here: https://youtu.be/QFhcsS8Bx-U
Figure 1: OData2SPARQL: the Janus-Point between RDF data stores and application development
Rapid Application Development Environments
There are a great number of superb application development frameworks that allow one to create cross platform (desktop, web, iOS, and Android), rich (large selection of components such as grids, charts, forms etc) applications. Most of these are based on the MVC or MVVM model both of which require a systematic and complete (CRUD) access to the back-end data via a RESTful API. Now that OData has been adopted by OASIS, the number of companies offering explicit support for OData is increasing, ranging from Microsoft, IBM, and SAP. Similarly there are a number of frameworks, one of which is SAPUI5 which has an open source version OpenUI5.
OpenUI5
OpenUI5 is an open source JavaScript UI library, maintained by SAP and available under the Apache 2.0 license. OpenUI5 lets you build enterprise-ready web applications, responsive to all devices, running on almost any browser of your choice. It’s based on JavaScript, using JQuery as its foundation, and follows web standards. It eases your development with a client-side HTML5 rendering library including a rich set of controls, and supports data binding to different models (JSON, XML and OData).
With its extensive support for OData, combining OpenUI5 with OData2SPARQL releases the potential of RDF Graph datasources for web application development.
Web IDE
SAP Web IDE is a powerful, extensible, web-based integrated development tool that simplifies end-to-end application development. Since it is built around using OData datasources as its provider, then WebIDE can be used as a semantic application IDE when the RDF Graph data is published via OData2SPARQL.
WebIDE runs either as a cloud based service supplied free by SAP, or can be downloaded as an Eclipse ORION application. Since the development is probably against a local OData endpoint, then the latter is more convenient.
RDF Graph application in 5 steps:
- Deploy OData2SPARQL endpoint for chosen RDF Graph store
The Odata2SPARQL war is available here, together with instructions for configuring the endpoints: odata2sparql.v2
The endpoint is this example is against an RDF-ized version of the ubiquitous Northwind databases. This RDF graph version can be downloaded here: Northwind
- Install WebIDE
Instructions for installing the Web IDE Personal edition can be found here: SAP Web IDE Personal Edition
- Add OData service definition
Once installed an OData service definition file (for example NorthwindRDF) can be added to the SAPWebIDE\config_master\service.destinations\destinations folder, as follows
Description=Northwind
Type=HTTP
TrustAll=true
Authentication=NoAuthentication
Name=NorthwindRDF
ProxyType=Internet
URL=http://localhost:8080
WebIDEUsage=odata_gen
WebIDESystem=NorthwindRDF
WebIDEEnabled=true
- Create new application from template
An application can be built using a template which is accessed via File/New/Project from Template. In this example the “CRUD Master-Detail Application” was selected.
The template wizard needs a Data Connection: choose Service URL, select the data service (NorthwindRDF) and enter the path of the particular endpoint (/odata2sparql/2.0/NW/).
Figure 2: WEB IDE Data Connection definition
At this stage the template wizard allows you to browse the endpoint’s entityTypes and properties, or classes and properties in RDF graph-speak.
Since the Web IDE and OpenUI5 is truly model driven, the IDE creates a master-detail given the entities that you define in the next screen.
The template wizard will ask you for the ‘object’ entityType which in this example is Category. Additionally you should enter the ‘line item’ but in this case there is only one navigation property (aka objectproperty in RDF graph-speak) which is the products that belong to the category.
Note that this template allows other fields to be defined, so titls and productUnitprice were selected.
Figure 3: WEB IDE Template Customization
- Run the application
The application is now complete and can be launched from the IDE. Right-click the application and select Run/Run as/As web application:
Figure 4: Application
Even this templated application is not limited to browsing data: it allows full editing of the categories. Note that even the labels are derived from the OData endpoint, but of course they can be changed by editing the application.
Figure 5: Edit Category
Alternatively a new category can be added:
Figure 6: Create New Category
Next Steps
That’s it: a fully functional RDF Graph web application built without a single line of code being written. However we can chose to use this just as a starting point:
- Publish data views, the SPARQL equivalent of a SQL view on the data, to the OData2SPARQL endpoint.
- These are particularly useful when publishing reports in OpenUI5, Excel PowerQuery, Spotfire, etc.
- Modify the model that is published via the OData2SPARQL endpoint
- The model that is published is extracted from the schema defined in the endpoint configuration. Thus the schema can be changed to suit what one wants in the endpoint metamodel.
- Edit the templated application
- The templated application is just a starting point for adaptation: the code that is created is nothing more than standard HTML5/JavaScript using the OpenUI5 libraries.
- Build the application from first-principles
- A template is not always the best starting point, so an application can always be built from first-principles. However the OpenUI5 libraries make this much easier by, for example, making the complete metamodel of the OData2SPARQL endpoint available within the application simply by defining that endpoint as the datasource.