An OLD web service consists of a data structure for storing the artifacts of linguistic fieldwork and analysis and a read-write interface to that data structure.

A major design principle of the OLD is that as much work as possible should be delegated to the user-facing applications so that the OLD web service can focus on providing secure and responsive multi-user concurrent access to a central data structure. In some cases, technological restrictions currently inherent to particular platforms (e.g., the inability of browser-based JavaScript applications to call external programs) have required server-side implementation of features that might otherwise be implemented client-side (e.g., morphological parsing, PDF creation using TeX).

The diagram below illustrates the core components of an OLD application.


When an OLD web application receives HTTP requests, the Routes component decides which Pylons controller will handle the request. This decision is based on the HTTP method of the request and the URL. Routes and the controllers conspire to create a RESTful interface to the data structure qua a set of resources. That is, a POST request to will be interpreted as a request to create a new form resource while the same URL with a GET method will be interpreted as a request to read (i.e., retrieve) all of the form resources. The first request will be routed to the create action (i.e., method) of the forms controller (i.e., class) while the second will be routed to the index action of that same controller. The authentication, authorization, input validation, data processing, linguistic analysis and database updates and queries are all handled by the controllers.

As illustrated in the diagram, the Routes and Controllers components can be conceptually grouped together as the interface of an OLD web service. The Interface section details this interface.

SQLAlchemy provides an abstraction over the tables and relations of the underlying database. Tables, their columns and the relations between them (i.e., the schema) are declared using Python data structures called models and interaction with the database is accomplished entirely via these. This not only simplifies interaction with the database (from the Python programmer’s point of view) but also makes it easier to use different RDBMSs (e.g., SQLite, MySQL) with minimal changes to the application logic.

As illustrated in the diagram, the Models and RDBMS components can be conceptually grouped together as the data structure of an OLD web service. The Data Structure section describes and argues for the utility of the data structure of the OLD.