Defining Base Views¶
Each source in the system is modeled as a series of base views. Each base view has attributes like a table in a relational database.
Each attribute of a view has a data type. The type of a specific attribute delimits which query operators can be applied to it and certain constraints that the elements of this type should comply with. The data types supported by Virtual DataPort are organized in two categories:
Normal: character strings, integers, floats, dates, etc.
Complex: array-type data (to represent multi-valued data) and register (to represent register-type data). By combining these two data types, Virtual DataPort represents hierarchical data structures like the ones obtained from an XML file.
In addition, each base view describes its query capabilities through its search methods. They define which queries can be executed over a base view. This is necessary because some data sources (e.g. Web sources or Web services) do not allow any type of query to be made on its data. Instead, they present limited interfaces (e.g. operations of a Web Service). If a base view does not have any search method, it cannot be queried.
Each search method is composed of a series of 5-uples. Each 5-uple represents a constraint that a specific query should comply with so that it can be executed on the source using this search method.
The format of a 5-uple is: attribute, operators, obligatoriness, multiplicity, possible values.
The section Search Methods of the Administration Guide explains in detail what search methods are.