A synonym. DODS uses aliases in its attribute-naming scheme. An attribute can have an alias, or second name, by which a user can identify it. An alias can have aliases of its own, but at this point, it becomes difficult to keep track of what points to whom, and we do not recommend this.
An API is simply a collection of functions and data types a program
uses to access some service. The data types and functions defined in
stdio.h, such as printf(), fseek(), FILE, and
fputc(), constitute a commonly used API for C program I/O. The
advantage of an API is that it insulates the user from the
implentation details of the program.
An array is an ordered set of variables. The members of a DODS array
must all be of the same data type. Array members may be accessed with
the [] operator. That is, array[4] specifies the fifth
member of array. Note that the index of the first array member
is zero. Arrays with multiple dimensions are defined as
single-dimensional arrays of arrays. For example, a two-dimensional
array is an array of arrays.
A quality of a data variable. This could be the method used to measure the variable's value, the name of the scientist who measured it, the color of the sky at the time, or whatever might be relevant.
A CGI program is a program that is executed by a httpd server upon receiving an appropriately configured URL. The DODS server is a CGI program. CGI is an Internet standard. DODS uses version 1.1.1 of the CGI standard.
A compound data type is one that is constructed from other data types. A compound type can be built from simple base types or from other compound data types. Arrays, Lists, Grids, Sequences, and Structures are all compound types, because they are all defined as aggregates of other data types.
A constraint expression is appended to a DODS URL to select data from the data set identified by the URL.
See Compound Data Type
A container attribute contains other attributes. The analogy is with a compound data variable, such as a Sequence or Structure, that contains other variables.
A daemon is simply a process that runs unattended on a UNIX computer.
An httpd server is generally run as a daemon. It's not clear how
the peculiar spelling came into use.
The DAP is the method a DODS client uses to retrieve data from a DODS server. The DAP consists of an intermediate data representation, an ancillary data format, a procedure for requesting the data from a server, and an API with which to execute the protocol.
This is a DODS construct, showing a list of variables, and attributes
associated with those variables, for a given data set. A variable's
attributes may include such things as the instrument that recorded it,
quality control information and so on. The response to a _das
request to a DODS server is a DAS.
This is a DODS construct, showing a textual representation of a data set's data model. The response to a _dds request to a DODS server is a DDS.
This is a JGOFS construct. The JGOFS API uses data set names instead of file names to refer to data sets. The API uses the data dictionary to look up the data set names, where it finds the file names or URLs to which the name refers.
The data model of a particular data set can be defined as the set of relationships between the variables that make up that data set. The important thing to remember is that it is this relationship that provides meaning to each of the numbers recorded in that data set. For example, without the relationship of the adjacent location measurement, a temperature measurement is just a number with no meaning.
A quantity of data, considered as a unit. A dataset may occupy one computer file, or several. A DODS dataset is a dataset that is served through a DODS server.
Distributed Oceanographic Data System. They wrote a book about it once.
A data attribute that applies to an entire dataset.
The Grid data type consists of an array with named dimensions, and a one dimensional array corresponding to each dimension. It is used to define data grids with irregular spacing.
The DODS core software can create a client-side sub-process with which to manage the user's screen display. Most clients adapted to using DODS will not be able to display intermediate results of a data query, nor will they be able to make sense of network error messages. The GUI manager creates a path whereby messages can travel from the DODS server to the DODS client core software to the user without returning to the client application. The DODS core software can also use the GUI manager by itself, without messages from the server.
Hyper-text Markup Language. This is the text formatting language in which web pages are written.
The httpd server is the web server. Web clients, such as browsers like Netscape or Mosaic, send messages to httpd servers on the machine identified in a URL. The return messages from these servers are the data that is displayed to the user.
The info service provides information about the usage of a
particular server. This is meant to include such information as any
functions defined by the server for use in constraint expressions,
error messages, the revision of the server software, and a list of any
data model translations defined for that server.
A method of evaluating a logical expression where evaluation halts after further evaluation could produce no change in the result. For example, when evaluating a string of sub-expressions linked by a logical AND, a lazy evaluator would halt after the first false sub-expression, because evaluation of subsequent sub-expressions would not change the result.
A List is an unordered list of variables. DODS list members must be of only one data type, but the type may be any of the base or constructor types.
A Sequence is a data type similar to a structure, but multi-valued. It is possible to think of a Sequence as an array of Structure values. Unlike an Array, however, only one value of the Sequence, corresponding to the Sequence state is available at any one time.
See Sequence. A sequence can be thought of as a multi-values structure. Unlike an array, where all the variable's values are available at once, the values of a sequence's members are only available for the current state. When the state advances, new variables become available.
A stride value is used to select a hyperslab from an array. If d
is a 10 by 10 array, then d[0:2:9][0:2:9] is a hyperslab
consisting of every second point in both dimensions.
The Structure data type is a set of variables, similar to a structure in the language.
A URL is a name that is unique across the Internet. It is analogous to a file name on a single machine in that it identifies some resource that might be data or a program.
See info service.