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== DAP4 Specification == | == DAP4 Specification == | ||
The draft specification has two volumes. | The draft specification has two volumes. | ||
# [http://dl.dropbox.com/u/53929684/dap4.docx Volume 1] is intended to specify the DDX syntax and semantics, the persistent representation, and the syntax and semantics of constraint expression. The initial draft of this volume can temporarily be accessed [http://dl.dropbox.com/u/53929684/dap4.docx here]. It will move to a more permanent location soon. | # [http://dl.dropbox.com/u/53929684/dap4.docx Volume 1] is intended to specify the DDX syntax and semantics, the persistent representation, and the syntax and semantics of constraint expression. The initial draft of this volume can temporarily be accessed [http://dl.dropbox.com/u/53929684/dap4.docx here]. It will move to a more permanent location soon. Last Modified: 5/25/2012. | ||
# Volume 2 is intended to specify the Web Services Components of the DAP4 protocol. That document has yet to be written. | # Volume 2 is intended to specify the Web Services Components of the DAP4 protocol. That document has yet to be written. | ||
Revision as of 19:12, 25 May 2012
OPULS Process
DAP4 Specification
The draft specification has two volumes.
- Volume 1 is intended to specify the DDX syntax and semantics, the persistent representation, and the syntax and semantics of constraint expression. The initial draft of this volume can temporarily be accessed here. It will move to a more permanent location soon. Last Modified: 5/25/2012.
- Volume 2 is intended to specify the Web Services Components of the DAP4 protocol. That document has yet to be written.
DAP4 Features
This is a straw man design, broken down into sections. It is incomplete and its content is subject to revision.
- Versions
- Checksum
- DAP Service Terminus
- Data Model and a XML Schema that provides one representation for the data model.
- Requests
- Responses
- Web Services
Proposals
Proposal | Status | Author | Date Proposed |
---|---|---|---|
Grids Ideas | Accepted | Dennis, et al. | (Cleaned up 4/10/2012) |
Old Version of Grids Proposal | Obsolete | Dennis | 4/10/2012 |
XML Use in DAP4 | Accepted | Dennis | 2/25/2012 |
Constraints and Shared Dimensions | Under Review, closely related to Grids Ideas | James & Dennis | Modified 04/12/2012 |
Ideas for Defining VLens (and Sequences) | Under Consideration | Dennis | 02/25/2012 |
Path Specification in DAP4 | New | Dennis | 3/30/2012 |
Coordinate Systems Element | New | Dennis | 4/10/2012 |
Nested Attributes | New | Dennis | 4/12/2012 |
Top Level Group | Accepted | Dennis | 4/12/2012 |
Subsetting Arrays and Grids By Value | New | Nathan | 4/27/2012 |
Proposal for a Constraint Notation | New | Dennis | 4/30/2012 |
Proposal for an Abstract Constraint Specification | New | James, ed. | 5/22/2012 |
Proposal for Structure Projection | New | Dennis | 5/1/2012 |
Proposal for Supporting Keys iin Sequences | Revised | Dennis | 5/24/2012 |
Proposal | Status | Author | Date Proposed |
---|---|---|---|
DAP4 DDX Grammar | New | Dennis | |
DAP4: DDX Lexical Elements | New | Dennis | 2/28/2012 |
Character Escape Mechanisms in DAP4 | New | Dennis | 4/5/2012 |
Proposed DAP4 On-The-Wire Format | New | Dennis | 4/8/2012 |
Proposed Multipart Mime Format | New | Dennis | 4/8/2012 |
Proposed Error Response Format | New | Dennis | 5/8/2012 |
Proposal | Status | Author | Date Proposed |
---|---|---|---|
Possible Notation for Server Commands | New | Dennis | Modified 04/12/2012 |
Asynchronous Responses | New | Nathan | 4/5/2012 |
DAP4 Capabilities and Versioning | New | EthanDavis | 4/10/2012 |
DAP4 Asynchronous Request-Response Proposal | New | EthanDavis | 4/10/2012 |
Commentary on DAP4 Related Topics
These are not intended as specific proposal, but rather as commentary on some issues with DAP4 that need addressing with specific proposals.
- Characterization of URL Annotations (Modified: 2/26/2012)
- Constructing a DDX from a Query (new: 04/12/2012)
- Notes on Constraints (new: 04/29/2012)
- DAP4: An Essay on Domain Specific Models (new: 05/05/2012)
OPULS Implementation Thoughts
Unidata's Current Thoughts
Unidata needs:
1) DAP4 C client library for use in netCDF-C library 2) DAP4 Java client library for use in netCDF-Java library 3) DAP4 Java server library for use in TDS 4) Conformance test service against which a DAP4 client library can be tested 5) Conformance test service against which a DAP4 server can be tested
The current CDM and TDS use of opendap-java library has performance problems due to extra API layers and extra copying of data. We would prefer direct serialization between CDM objects and the DAP on-the-wire data and would recommend that the OPeNDAP Java library leverage the netCDF-Java libraries.
If there are needs that the DAP4 opendap-java library be independent of the netCDF-Java library, then in order for CDM and TDS to use the opendap-java library, we would need the performance concerns mentioned above addressed. A reasonable metric would be within some percentage of cdmremote[1], say within 20-25%.
Unidata's performance requirements for Java libraries:
1) The netCDF-Java library performance reading DAP4 through the DAP4 Java client library must perform within 20-25% of cdmremote [1]. 2) TDS performance when handling DAP4 requests using the DAP4 Java server library should perform within 20-25% of cdmremote [1].
We believe this means that the DAP4 Java libraries must provide a sufficiently generic API that can be used directly with the CDM/TDS IOSP interface.
Unidata will:
1) Write the DAP4 C client library. 2) ??? some part of Java server library 3) ??? some parts of conformance testing services
NOTES:
[1] cdmremote is an experimental CDM streaming service. It is basically a direct serialization of the CDM.
OPULS references
Old DAP4 Design and Implementation
- DAP3/4
- DAP 4.0 Design and DAP 4.0 Essential Features The design is meant to be a complete document while essential features are the minimal see we want to release. Since this task has been stalled for nearly a year, doing the latter seems like a noble goal.