4.1 Selecting Data: Using Constraint Expressions

The URL such as this one:

http://dods.gso.uri.edu/cgi-bin/nph-nc/data/buoys.nc

refers to the entire dataset contained in the buoys.nc file. A user may, however, choose to sample the dataset simply by modifying the submitted URL. The constraint expression attached to the URL directs that the data set specified by the first part of the URL be sampled to select only the data of interest from a dataset even for programs that do not have a built-in way to accomplish such selections. This can vastly reduce the amount of data a program needs to process, and reduce the network load of transmitting that data to the client.

• 4.1.1 Constraint Expression Syntax
  • Simple Constraint Expression Examples
• 4.1.2 Operators, Special Functions, and Data Types
• 4.1.3 Using Functions in a Constraint Expression
• 4.1.4 Using URLs in a Constraint Expression
  • Examples
• 4.1.5 Pattern Matching with Constraint Expressions
  • Examples
• 4.1.6 Optimizing the Query