DAP4 Web Services v3

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Introduction

This document provides a detailed discussion of the web services (i.e. the structure of the request and response messages) which DAP4-compliant software MUST support when utilizing the HTTP protocol to transmit DAP requests and responses, along with additional optional services that it SHOULD support.

The DAP4 protocol uses three basic responses to represent a data resource. One response, the Dataset Metadata (DDX) response returns metadata information describing the structure of the data resource. That is, it characterizes the variables, their datatypes, names and attributes. The second response, the Data (DataDDX) response, returns both the metadata about the request, but also the data that was requested. The Dataset Metadata response and the metadata part of the DataDDX are represented using a specific XML representation. The syntax of the Dataset Metadata response/document is described in the DAP4 Data Model Specification. The third basic response is the Dataset Services response that provides a listing of services, any alternate media representations if available, and all of the associated access URI's for a particular data resource.

Each of the three responses (Dataset Metadata, Data, and Dataset Services) are complete in and of themselves so that, for example, the Data response can be used by a client without ever requesting either of the two other responses. In many cases, client programs will request the Dataset Metadata response before requesting the Data response but there is no requirement they do so and servers SHALL NOT require that behavior on the part of clients. Operationally, communication between a DAP4 client and a DAP4 server utilizes some underlying already existing protocol. This, as previously mentioned, document defines the way in which the DAP4 protocol utilizes the HTTP protocol.

Access to each of these three responses is clearly defined by a combination of a Data Resource URL plus a well known suffix. When handed a DAP4 data resource URL any human, or their software agent, can easily obtain any of the three responses without first having to ask the server for one of the other responses.

The DAP4 protocol returns error information using an Error response. If a request for any of the three basic responses cannot be completed then an Error response is returned in its place.

The core DAP4 resource types and their representations are documented in the following DAP4 documents:

• DAP4 Dataset Services
• DAP4 Data Model, which contains:
  • Constraint Expressions
  • the DAP4 Dataset Description document (DDX) and it's XML representation
  • the DAP4 Data object (DataDDX) and it's binary encoding.

Several types of extensions can be made to the DAP4 core including:

• new encodings for the core DAP4 resource types;
• new resource types; and
• new server-side functions.

The DAP4 web service is currently limited to HTTP GET requests though it is expected that extensions (e.g., asynchronous access) will use other HTTP methods (e.g., POST). This makes, for now, the DAP4 Constraint Expression something of a pseudo-resource type given that they are encoded as part of the URL query string rather than as an independent document.

HTTP

The DAP4 Web Services specification describes the features of HTTP that are required to be a compliant DAP4 client or server. It does not attempt to describe all aspects of HTTP that DAP4 servers might implement or that DAP4 clients may see in response to DAP4 requests. Similarly, it does not cover all issues related to the performance and scalability of HTTP.

However, the following sections include both DAP4 requirements as well as some suggestions of HTTP features that servers and clients are encouraged to use.

Content Negotiation and Media Types

Though the DAP4 core specifications only describe one encoding for each type of resource, DAP4 web servers MAY have the ability to provide a given resource in a number of different media types. All media types available for a resource MUST be listed in the DAP4 Dataset Services response document.

DAP4 responses SHOULD use the "Content-Type" header field to identify the media type of the DAP4 response body. For example, the value for an XML encoded DDX response is "application/vnd.org.opendap.ddx+xml".

The DAP4 Dataset Services response describes the available services and their media types and provides DAP4 software (client and/or server) two different mechanisms to negotiate for different kinds of media representations. The first of these is server-driven content negotiation as described in the HTTP 1.1 specification, section 12 "Content Negotiation". The second is similar to the agent-driven negotiation also described in section 12 of the HTTP 1.1 specification. The difference being that the "list of available representations ... [each with] its own URI" is provided by the DAP4 Dataset Services response rather than in response to an initial request.

Clients need not retrieve the Dataset Services response in order to access the normative representations of either the Dataset Metadata or Data responses, as these responses are required for every DAP4 server and are mapped to well known URL patterns. If clients attempt to access other representations or other services using agent-driven negotiation without first checking the Dataset Services response, they should be prepared to receive a 404 Not Found response.

When using server-driven negotiation, DAP4 clients are encouraged to, at a minimum, include "Accept" and "User-Agent" headers in their requests and to provide accurate and detailed information in the values of those headers. However, when server-driven negotiation is used, DAP4 servers are not limited to those headers for determining the media type that is returned. DAP4 clients should also be prepared to handle 415 "Unsupported Media type" response codes.

When DAP4 servers engage in server-driven content negotiation they SHOULD only return DAP4 media types to clients that explicitly request them, otherwise they should return the most general media type that correctly represents the response content. In particular if a DAP4 server detects that a general purpose web browser (such as Internet Explorer, Firefox, Chrome, Safari, Opera, etc.) is requesting one of the three DAP4 response types then the Content-Type header in the servers response SHOULD be the most widely understood media type for the particular response. For the Dataset Services response and Dataset Metadata response this would be a media type of text/xml and for the Data response it would be multipart/mixed. This is particularly important for the Dataset Services response and Dataset Metadata response as these XML documents may come with XSLT style sheet references that would allow the browser to transform the XML content into an HTML presentation suitable for the browsers. This presentation may even include a complete data request form that will allow the user to subset and select data in their browser. If the DAP4 specific media types are returned the browsers will simply write the response to disk and they will make no effort to render the response in the browser using the stylesheet reference.

Redirects

While HTTP redirects are not directly part of the DAP4 web protocol it is strongly suggested that DAP4 client implementations be capable of processing HTTP redirects as nominally described in the HTTP specification sections on redirection status codes and response headers (It is suggested that implementers of DAP4 clients utilize an existing robust HTTP client library that will manage this for them.)

Caching of Responses and Conditional Requests

While, HTTP caching and conditional requests are not explicitly part of the DAP4 web protocol, they do provide important tools for improving the performance of both sides client server interaction. Therefore, it is strongly suggested that DAP4 servers and client implementers be aware of how HTTP caching works, and utilize it for working with DAP servers.

Authentication/Authorization

Authentication is the process by which a user agent establishes the identity of the user to a server, and the server establishes it's identity with the user agent. While, HTTP authentication is not explicitly part of the DAP4 web protocol, it does provide important tools for securing the client server interaction. Therefore, it is strongly suggested that DAP4 servers and client implementers be aware of how HTTP authentication works, and utilize it for working with DAP servers. Server implementers should pay particular attention to HTTP security considerations.

Authorization is the process through which a server determines who/what has access to its various holdings and services. The HTTP protocol does not directly address the issue of authorization (even though HTTP defines the 401 response status using the word "authorization" it does not provide separate semantics for authentication and authorization which we see as an important distinction for data access) (Is this true? I'm pretty sure it is... ndp), but any DAP4 server implementer should be aware that some kind of mechanism for controlling access to holdings and services will likely be desired by the people that install and operate their software.

Headers

Request Headers

These are the HTTP request headers that DAP clients using HTTP MAY utilize. DAP4 servers MUST accept these headers and act on them in a manner consistent with their descriptions below.

General

Accept

The HTTP Accept header MAY be used by clients that wish to engage in server-dirven content negotiation by requesting a particular representation of a resource in the initial request. The server MUST utilize this header, if present, in a manner consistent with the HTTP content negotiation specification.

User-Agent

The HTTP User-Agent header MAY be used by clients to indicate their "software identity" to the server. The server MAY utilize this header, if present, to alter the Content-Type of the response to something that is more likely to be digestible by the requesting client software.

DAP Specific

There are no DAP specific headers required to make a general DAP request.

Asynchronous Transaction

X-DAP-Async-Accept

A client MAY indicate it's willingness to accept asynchronous responses by including the X-DAP-Async-Accept HTTP header. Clients MAY make conditional requests for asynchronous responses by indicating the maximum time they are willing to wait by using the X-DAP-Async-Accept HTTP header with a value given in seconds. A value of zero indicates that the client is willing to accept whatever delay the server may encounter.

Response Headers

These are the HTTP response headers that DAP servers using HTTP MUST and SHOULD (as indicated) return.

General

Date

DAP4 servers MUST return an HTTP Date header whose value is the time of the response and which MUST be in RFC 1123 format.

Last-Modified

DAP4 servers SHOULD return an HTTP Last-Modified header whose value is the last modified time of the request resource and which MUST be in RFC 1123 format.

Content-Type

DAP4 servers MUST return an HTTP Content-Type header, the value of which SHOULD be set in accordance with the Media Types discussion above.

Content-Description

DAP4 servers SHOULD return an HTTP Content-Description header.

Content-Disposition

DAP4 servers SHOULD return an HTTP Content-Disposition header when transmitting file typed responses.

Content-Encoding

DAP4 servers MUST return an HTTP Content-Encoding header when the content-coding of an entity is not "identity".

DAP Specific

X-DAP-Server

DAP4 servers SHOULD return the X-DAP-Server HTTP header. This HTTP header is used in a response to communicate the software version of the server. This may be a simple string with the server name and version number, or multiple software component versions may be represented. The value of this header is a string determined by the implementations author(s).

Example

X-DAP-Server: bes/3.10.0, libdap/3.11.2, dap-server/ascii/4.1.2, csv_handler/1.0.2, freeform_handler/3.8.4, fits_handler/1.0.7, fileout_netcdf/1.1.2, gateway_module/1.1.0, hdf4_handler/3.9.4, hdf5_handler/1.5.0, netcdf_handler/3.10.0, ncml_module/1.2.1, dap-server/usage/4.1.2, dap-server/www/4.1.2, xml_data_handler/1.0.1

Example

X-DAP-Server: TDS-4.19.3

X-DAP

DAP4 servers MUST return the X-DAP HTTP header. This HTTP header is used in a response to indicate the DAP protocol version used to encode the content of the response. This value is constrained to a format of "major_version" dot "minor version", where both major_version and minor_version are represented by an integer value.

Example

X-DAP: 4.0

Example

X-DAP: 2.17

Asynchronous Transaction

X-DAP-Async-Required

DAP4 servers MUST return the X-DAP-Async-Required header if the request requires an asynchronous response and the client has not indicated willingness to accept such a response. Rejection of the request should also be indicated by the 400 DAP Asynchronous Response Required HTTP response code.

Status Codes

DAP servers that provide an HTTP interface are expected to utilize the HTTP response codes in a manner consistent with the HTTP 1.1 specification.

The ones that are detailed here are used by the DAP in a manner consistent with the specifications definition, but in support of specific DAP server behavior.

200 OK

A server MUST return an HTTP status of 200 when the request has been successful and that the returned document contains the requested resource. However since DAP responses can be quite large and since it is also possible for the server to encounter any number of problems during the marshaling, serialization, and subsequent transmission of the response it is possible that the server may have committed/transmitted the HTTP headers (in which the status value is transmitted) before a subsequent error is encountered. These types of errors are transmitted in the DAP4 over-the-wire protocol and all DAP4 clients MUST be able to read and process these errors. See Section?

202 Accepted

A server MUST return a 202 Accepted HTTP response code when a request has been accepted and will be handled asynchronously. The response body MUST contain a DAP asynchronous response document.

400 Bad Request

The HTTP specification defines this status code as:

The request could not be understood by the server due to malformed syntax. The client SHOULD NOT repeat the request without modifications.

DAP servers utilizes this code to mean one of two things.

400 Bad DAP4 Request Syntax

The 400 Bad DAP4 Request Syntax HTTP response code MUST be returned by the server when there is a problem with the syntax of the OPeNDAP URL. The problem could be in the formulation of the constraint expression, or it may be that the URL extension did not match any that are known by this server

400 DAP4 Asynchronous Response Required

The 400 DAP4 Asynchronous Response Required HTTP response code MUST be returned by the server when the DAP request has been rejected because an asynchronous response is required and the client did not indicate willingness to accept an asynchronous response. The server MUST include the X-DAP-Async-Required HTTP header and the DAP4 Asynchronous Response Required document as the response body.

401 Unauthorized

The 401 Unauthorized HTTP response code MUST be returned by the server when access to the requested resource requires (not previously acquired) user authentication. See the HTTP specification for usage and behavior.

403 Forbidden

The 403 Forbidden HTTP response code MUST be returned when the server has understood the request, but is refusing to fulfill it. Authorization will not help and the request SHOULD NOT be repeated. This is appropriate to return if, for example, the server software does not have read permission for the requested resource.

404 Not Found

The 404 Not Found HTTP response code MUST be returned when the server has not found anything matching the Request-URI.

409 Conflict (DAP Async Response Not Available)

The 409 Conflict HTTP response code SHOULD be returned by the server when the DAP request has been rejected because a previous asynchronous request has not been completed and the result is not ready for access. The response body MUST contain the DAP4 Asynchronous Response Not Yet Available document.

412 Precondition Failed

The 412 Precondition Failed HTTP response code MUST be returned by the server if the DAP request has been rejected because it did not meet the X-DAP-Async-Accept condition that was specified in the request. The response body MUST contain the DAP4 Asynchronous Request Rejected document.

415 Unsupported Media Type

The 415 Precondition Failed HTTP response code MUST be returned when the client requests a representation of the requested resource that the server cannot provide.

500 Internal Server Error

The 500 Internal Server Error SHOULD be returned when the DAP server encounters problems internal problems when attempting to fulfill a request.

Verbs (aka Methods)

GET

A DAP request may be made using the HTTP GET request method utilizing a Uniform Resource Identifier (URI) that encodes information specific to the DAP (see Section ?).

Each GET request MUST conform to the HTTP specification (which basically says that a GET request MUST contain an HTTP protocol version number followed by a MIME-like message containing various headers that further describe the request.). While there are some optional DAP HTTP request headers that may be used, DAP requests do not require specific HTTP headers beyond those necessary for HTTP. DAP servers SHOULD support the use of the HTTP Accept request header to allow clients to engage in HTTP content negotiation for specific representations of a DAP response.

Implementation Note

In practice, DAP clients typically use a third-party library implementation of HTTP/1.1 so the GET request, URI and HTTP version information are hidden from the client; it sees only the DAP Uniform Resource Locator (URL) and the request headers.

The DAP server responds to the GET request with an HTTP compliant response (one that includes a status line containing the HTTP protocol version and an error or success code, followed by HTTP response headers and then response itself). There are two DAP specific HTTP headers that are always included in a DAP response over HTTP: X-DAP-Server and X-DAP, as described above. The DAP response is the payload of the HTTP response. Unless otherwise negotiated, the data response payload is encoded in multpart-MIME format, while the other responses are simple HTTP responses This is further described in Section ?.

Examples

HTTP GET request.

GET /dap/path/data.nc.dap?u,v[0:8:1024] HTTP/1.1
Host: server.org
Accept: application/x-dap4

Web Services

The DAP web services are all defined as extensions to the data resource (aka base) URL. This data resource URL essentially becomes a prefix (and could even be seen as a namespace) for all of the services available for that data resource.

A Service is represented by:

• A unique "namespace" like identifier that is used to define an xlink:role attribute.
• A simple human readable name called 'title'.
• An access URL and a media-type describing the response.
• An optional description.

A service is accessed by dereferencing its access URL, which is typically constructed by adding some type of suffix to the data resource URL. The way in which the query string (aka constraint expression) is used is defined by each service, and there is no requirement for inter-service query string API conformity.

Primary DAP4 Services

These three primary DAP4 services MUST be provided for each dataset served by a DAP4 compliant server.

All of the example requests described below are based on the data resource URL:

http://server.org:8080/dap/path/data.nc

Note regarding JSON responses

In the following we describe two media types in most cases: the primary media type (e.g., text/xml) and application/json. We have not defined how those JSON, BJSON, Universal binary JSON, ..., responses will be formatted.

For the JSON media type for the data response, we might look at http://ubjson.org/. However, I think JSON support is one place where we could get some solid input from the community.

DAP4 Dataset Services

The DAP Dataset Services response provides a listing of the various web services and their associated media-type representations available for a dataset. Dereferencing the base URL for a dataset accessed through a DAP4 web server will return a DatasetServices document that describes the various responses possible for that data set, including URLs that can be used to access those responses. In other words, the Dataset Services response is acquired by dereferencing the data resource (aka base) URL for the dataset and there is no suffix added to the data resource URL prior to that dereferencing.

Every DAP4 compliant server MUST return the normative representation (an XML document as described here section) of the Dataset Services response when a client attempts to access an unmodified dataset URL. The DAP4 server MAY return alternate representations if the client indicates that it can accept them and the server can provide them.

More information on the Service Description response can be found on the DAP4 Dataset Services page.

service suffix =
service url = dataset_url
role id = http://services.opendap.org/dap4/dataset-services#

DAP4 media type:

• application/vnd.org.opendap.dap4.dataset-services+xml
  

Most general applicable media type:

• text/xml
  

Optional media type(s):

• application/json
  

url = dataset_url.json

HTTP Request Examples

Simple

This simple request will return the XML representation of the Dataset Web Services response.

GET /dap/path/data.nc HTTP/1.1
Host: server.org:8080
Accept: */*

Server-driven content negotiation

Client requests the Dataset Services response and indicates that it wants the JSON representation. The server SHOULD reply with the JSON representation if it is available, otherwise it may return it's default XML representation.

GET /dap/path/data.nc HTTP/1.1
Host: server.org:8080
Accept: application/json

Agent-driven content negotiation

Client requests the JSON representation of the Dataset Services response. The server MUST reply with the JSON representation if available, or with a status of 404 if not.

GET /dap/path/data.nc.json HTTP/1.1
Host: server.org:8080
Accept: */*

DAP4: Dataset Metadata Service

The Dataset Metadata Service returns the Dataset Metadata Response (DMR) which is a metadata description of the dataset. The normative representation of the DMR is an XML document that contains both the 'syntactic' (structural) and 'semantic' metadata for the dataset, persisted as a DAP4: Data Model representation of the dataset held at the server. The Dataset Metadata service accepts a query string (constraint expression) that allows you to inspect the effects on the data structures when sub-setting and/or server side functions are applied. If a constraint expression has been successfully applied, the service will returned the constrained view of the dap:Dataset object. The constrained view may contain different data structures than the unconstrained view as the constraint may alter the reasonable representation of the data set. Note that All dap:Attribute objects have been removed from constrained dap:Dataset objects.

Every DAP4 compliant server MUST return the normative representation (an XML document as described here ) of the Dataset Metadata Response when a client attempts to access a dataset URL with the suffix ".dmr" appended to it. The DAP4 server MAY return alternate representations if the client indicates that it can accept them and the server can provide them.

• More information on the DMR can be found on the DAP4: Responses page.

• More information on the syntax of DAP4 constraint expressions can be found on DAP4: Data Model page.

service suffix = .dmr
service url = dataset_url + '.dmr' + [?dap_constraint]
role id = http://services.opendap.org/dap4/dataset#

DAP4 media type:

• application/vnd.org.opendap.dap4.dmr+xml
  

Most general applicable media type:

• text/xml
  

Optional media type(s):

• application/json
  

url = dataset_url.dmr.json[?dap_constraint]

HTTP Request Examples

Simple

This simple request will return the XML representation of the Dataset Metadata response with a Content-Type of text/xml

GET /dap/path/data.nc.xdp HTTP/1.1
Host: server.org:8080
Accept: */*

DAP4

This DAP4 request will return the XML representation of the Dataset Metadata response with a Content-Type of application/vnd.org.opendap.ddx+xml

GET /dap/path/data.nc.xdp HTTP/1.1
Host: server.org:8080
Accept: application/vnd.org.opendap.ddx+xml

Server-driven content negotiation

Client requests the dataset metadata response and indicates that it wants the JSON representation. There server SHOULD reply with the JSON representation if it is available, otherwise it may return it's default XML representation.

GET /dap/path/data.nc.xdp HTTP/1.1
Host: server.org:8080
Accept: application/json

Agent-driven content negotiation

Client requests the JSON representation of the dataset metadata response. The server MUST reply with the JSON representation if available, or with a status of 404 if not..

GET /dap/path/data.nc.xdp.json HTTP/1.1
Host: server.org:8080
Accept: */*

DAP4: Data Service

The Data Service provides DAP4 data access to a dataset, and is the way that DAP4 returns data to a client. The Data service accepts a query string (constraint expression) which allows you to subset the data and invoke server side functions. When the service is invoked it returns the DAP4 data object. On the wire this is a multipart MIME document where the first MIME part contains the constrained Dataset response describing the data requested and the following MIME parts contain the data values, encoded using XDR, followed by a checksum, for each variable in the dataset.

Every DAP4 compliant server MUST return the normative representation (an multi-part MIME document as described here ) of the Data Response when a client attempts to access a dataset URL with the suffix ".dap" appended to it. The DAP4 server MAY return alternate representations if the client indicates that it can accept them and the server can provide them.

More information on the Data response can be found on the DAP4: Responses page.

suffix = .dap
service url = dataset_url + '.dap' + [?dap_constraint]
role id = http://services.opendap.org/dap4/data#

DAP4 media type:

• application/vnd.org.opendap.dap4.data
  

Most general media type:

• multipart/mixed
  
  • First Part: text/xml
    
  • Second Part: application/octet-stream
    

Optional media type(s):

• application/json This Needs Elaboration - what do we mean here? A single JSON document? Replacing the DDX in part 1 with JSON?

url = dataset_url.dap.json[?dap_constraint]

HTTP Request Examples

Simple

This simple request will return the full contents of the dataset resource as a DAP4 data object.

GET /dap/path/data.nc.dap HTTP/1.1
Host: server.org:8080
Accept: */*

Server-driven content negotiation

Client requests the DAP4 data response and indicates that it wants the JSON representation. There server SHOULD reply with the JSON representation if it is available, otherwise it may return it's default XML representation.

GET /dap/path/data.nc.dap HTTP/1.1
Host: server.org:8080
Accept: application/json

Agent-driven content negotiation

Client requests the JSON representation of the DAP4 data response. The server MUST reply with the JSON representation if available, or with a status of 404 if not..

GET /dap/path/data.nc.dap.json HTTP/1.1
Host: server.org:8080
Accept: */*

Other DAP4 Services

DAP4: HTML DATA Request Form Service

The HTML DATA Request Form Service provides browser based access to the Dataset. When invoked it returns a web-browser renderable document (in html) that provides a form (or other UI) that can be used to constrain and request data in accordance with the DAP4 specification as applied to the dataset .

suffix = .html
service url = dataset_url + .html
role id = http://services.opendap.org/dap4/data-request-form#

Default/primary media type: text/html | text/xhtml

DAP4: RDF Service

The RDF service provides an RDF representation of the Dataset document (DDX). The RDF response is an XML document containing an RDF version of the DAP4: Dataset Response.

suffix = .rdf
service url = dataset_url + .rdf
role id = http://services.opendap.org/dap4/rdf#

Default/primary media type: application/rdf+xml

DAP4: ISO 19115 Service

This service provides ISO 19115 metadata for the Dataset, if any can be found. When invoked it returns an XML document containing ISO 19115 metadata located in the DAP4: Dataset Response.

suffix = .iso
service url = dataset_url + .iso
role id = http://services.opendap.org/dap4/iso-19115-metadata#

Default/primary media type: text/xml

DAP4: ISO Conformance Score Service

This service provides a browser renderable document that describes how well the metadata held in the Dataset conforms to ISO 19115. When invoked this service returns a browser renderable document that scores how well the metadata held in the Dataset Response conforms to ISO 19115.

suffix = .rubric
service url = dataset_url + .rubric
role id = http://services.opendap.org/dap4/iso-19115-score#

Default/primary media type: text/html

DAP4: NetCDF File-out Service

This service provides data responses in NetCDF-4 file format. When invoked the regular DAP data response will be repackaged as a NetCDF 4 file.

suffix = .nc4
service url = dataset_url + '.nc4' + [?dap_constraint]
role id = http://services.opendap.org/dap4/netcdf-3#

Default/primary media type: application/x-netcdf-4

DAP4: ASCII Data Service

This service provides data responses in ASCII format. When invoked the regular DAP data response will be repackaged as an ASCII representation of the data values.

suffix = .ascii
service url = dataset_url + '.ascii' + [?dap_constraint]
role id = http://services.opendap.org/dap4/ascii#

Default/primary media type: text/plain

DAP4: XML Data Service

This service provides data responses in XML format. When invoked the constrained Dataset response document (DDX) will be marked up with the data values of the request and returned. Large requests may be denied.

suffix = .xdap
service url = dataset_url + '.xdap' + [?dap_constraint]
role id = http://services.opendap.org/dap4/xml-data#

Default/primary media type: text/xml

DAP4: Native File Access Service

This service provides direct access to the data source file (or whatever else) that is creating the DAP dataset resource. When invoked it returns the "native" data from whatever store (filesystem, etc.) it may be in.

suffix = .file
service url = dataset_url + .file
role id = http://services.opendap.org/dap4/file#

Default/primary media type: Type varies with file type.

DAP4: Server Version Service

This service provides software versioning information. When invoked the services returns an XML file containing a description of the version of the server and it's components.

suffix = .ver
service url = dataset_url + .ver
role id = http://services.opendap.org/dap4/version#

Default/primary media type: text/xml

DAP2 Services

DAP2: Data Service

The DAP2 data service provides DAP2 data access to the data resource.

suffix = .dods
service url = dataset_url + '.dods' + [?dap_constraint]
role id = http://services.opendap.org/dap2/dods#

Default/primary media type: application/octet-stream

DAP2: DDX Service

The DAP2 DDX service provides DAP2 access to the data resource metadata. When invoked the service returns an XML document containing both syntactic and semantic dataset metadata in DAP2 XML format.

suffix = .ddx
service url = dataset_url + .ddx
role id = http://services.opendap.org/dap2/ddx#

Default/primary media type: text/xml

DAP2: DDS Service

The DAP2 DDS service provides access to the 'syntactic' metadata (aka use or structural metadata) for the data resource. When invoked returns a DAP2 DDS response document conforming to the DDS part of the DAP2 specification.

suffix = .dds
service url = dataset_url + '.dds' + [?dap_constraint]
role id = http://services.opendap.org/dap2/dds#

Default/primary media type: text/plain

DAP2: DAS Service

The DAP2 DAS service provides access to the 'semantic' metadata (aka domain metadata) for the data resource. When invoked returns a DAP2 DAS response document conforming to the DAS part of the DAP2 specification.

suffix = .das
service url = dataset_url + .das
role id = http://services.opendap.org/dap2/das#

Default/primary media type: text/plain

DAP2: Info Service

The DAP2 INFO service provides a browser renderable page that combines both the DAP2 'syntactic' and 'semantic' metadata for the data resource in a human readable way. When invoked this service returns a web browser renderable document that combines both the DAP2 'syntactic' and 'semantic' metadata for the data resource in a human readable way.

suffix = .info
service url = dataset_url + .info
role id = http://services.opendap.org/dap2/Info#

Default/primary media type: text/html

DAP2: NetCDF Service

This service provides data responses in NetCDF-3 file format. When invoked the regular DAP data response will be repackaged as a NetCDF 3 file.

suffix = .nc
service url = dataset_url + '.nc' + [?dap_constraint]
role id = http://services.opendap.org/dap4/netcdf-3#

Default/primary media type: application/x-netcdf

Template: ServiceTemplate