APAC, Perth, WA 20071012 1 OPeNDAP (The Open-source Project for a Network Data Access Protocol) APAC Tutorial October 12, 2007 [email protected]

APAC, Perth, WA 20071012

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OPeNDAP(The Open-source Project for a Network Data Access Protocol)

APAC Tutorial October 12, 2007

[email protected]


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Some DefinitionsDAP = Data Access Protocol

Model used to describe the data; Request syntax and semantics; and Response syntax and semantics.

OPeNDAP The software; Numerous reference implementations; Core/libraries and services.

OPeNDAP Inc. OPeNDAP is a 501 c(3) non-profit corporation; Formed to maintain, evolve and promote the

discipline neutral DAP that was the DODS core infrastructure.


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Some DefinitionsSyntax

The computer representation of a data object - the data types and structures at the computer level; e.g.,

T is a floating point array of 20 by 40 elements.

Semantics The information about the contents of an object; e.g., T is sea surface temperature in degrees Celsius for a

certain region of the Earth.


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Distributed Oceanographic Data System

(DODS) Conceived in 1993 at a workshop held at URI.

Objectives were:– to facilitate access to PI held data as well as data held

in national archives and– to allow the data user to analyze data using the

application package with which he or she is the most familiar.

Basic system designed and implemented in 1993-1995 by Gallagher and Flierl with NASA and NOAA funding.

From 1994 to present it has been extended with NASA, NOPP, NSF and NOAA funding.


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Considerations with regard to the development of OPeNDAP

Many data providers

Many data formats

Many different semantic representations of the data

Many different security requirements

Many different client types


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Broad Vision

A world in which a single data access protocol is used for the exchange of data between network based applications regardless of discipline.

A layer above TCP/IP providing for syntactic and semantic consistency not available in existing protocols such as FTP.


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Practical Practical Considerations

The broad vision:

Is syntactically achievable, but

Is not semantically achievable, at least not in the near term.


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OPeNDAP Mission Statement

To maintain, evolve and promote a data access protocol (DAP) for the syntactically consistent exchange of data over the network.

The DAP should provide syntactic interoperability across disciplines and allow for semantic interoperability within disciplines*****.


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OPeNDAP Vision StatementTo achieve the mission:

OPeNDAP will be Non-profit. Easier to obtain federal funds. The DAP is more likely to be adopted.

OPeNDAP software will be open source. More likely to be adopted. Need community contributions to software.

OPeNDAP will mix implementation with research. Implementation - to encourage use. Research - to keep the protocol current.


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OPeNDAP Vision Statement (cont)

OPeNDAP will rely primarily on federal funding. Unlikely to obtain private funding for middleware. Development to be use case driven. Aligned with Vision/Mission.

Strategic direction will be sought from an Advisory Board consisting of data system experts and with input from you the community of developers.

OPeNDAP will seek partners.

OPeNDAP will utilize community working groups to develop ‘standards’ related to the DAP, OPeNDAP


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OPeNDAP tactics• The fundamental objective of OPeNDAP and

OPeNDAP Inc. is to facilitate internet access to scientific data

• This is done by:– Providing a protocol (DAP) to access data over the internet,– Hiding the format (and organization) in which the data are

stored from the user, and– Providing subsetting (and other) capabilities for the data at

the server

• OPeNDAP is based on a multi-tier architecture• OPeNDAP software is open source• Working groups formed on specific topics


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OPeNDAP relies on projects

• To guide user-based requirements for application needs as well as OPeNDAP core development (use cases)

• To provide maintenance and evolution of the core software and documentation

• Currently: 7 active projects, covers next ~2-3 years, 2 pending proposals

• ……


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SuccessWhat constitutes success of the OPeNDAP mission?

Adoption of the DAP across a broad range of disciplines with extensive use in several of these.

In order to achieve this the DAP must do the following:

It must be sufficiently flexible, all encompassing, etc. that it can be used across a broad range of data types.

Its implementation must be robust, secure, easy to use, provide for a broad range of services, etc.

The funding stream must be robust.

Active and engaged developer and user community


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Risks

It is still the case that

Some other data access protocols are seen as more attractive regardless of whether or not they are, or

Other data access protocols are developed because their community is not aware of OPeNDAP or of what its capabilities are.

We will compare and contrast some of these today


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To SucceedOPeNDAP must make sure that:

It’s (server and client) capabilities are well known across a broad range of disciplines.

The data model is inclusive.

The implementation is robust and meets user’s needs.

The DAP coexists with other protocols.

It has a robust funding base.

It has extensive documentation.


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Robust Funding?What is an appropriate level of activity (funding) for OPeNDAP? What should OPeNDAP be doing?

Core only? + Clients and servers? + Demonstration projects?

Should OPeNDAP be a small staff (core only) or…?

What priority should be assigned to the elements currently being developed? Which of these go beyond the core?

DAP4

AIS - metadata consistency

THREDDS - Catalogs

Toolkits - Matlab, IDL,…

Grid capabilities

OTHERS?


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Releases/Support

Periodic releases User services - OPeNDAP ([email protected])

User support - first line of defenseManages the opendap-dev discussions


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Binaries Generated

There are approximately 80 binaries built on a nightly basis. They are built for the following platforms/operating systems:

Linux FC4 FC5

MacOS-X (universal binaries when possible)

Windows XP, win32

Java 1.5 (Tomcat 5.5)

IRIX (in four variants), Solaris, AIX, OSF


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Communication Website (http://www.opendap.org and test.opendap.org) SVN - Code repository

(http://scm.opendap.org:8090/trac/browser/) Trac - Task/milestone repository

(http://scm.opendap.org:8090/trac/) Telecons

Management - Weekly Developers - Weekly on Monday 11am MT

Twiki -> MediaWiki Management Developers Coming soon http://docs.opendap.org

opendap-dev e-mail list - main mechanism for messages

http://www.opendap.org/

http://docs.opendap.org/


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OPeNDAP Community Working Groups Modeled after best practices of IETF, W3, OGC, IEEE,

ISO, and others Working Groups:

Authentication Security Server-side Functions Virtualization (Aggregation) Server-side processing Geospatial Interoperability Hyrax and *DS (TDS, GDS, FDS, etc.) Semantics DAPPER netCDF C++ client Response types Metrics Asynchronous transactions DAP4 Relational Database access via DAP

Wiki (http://docs.opendap.org/index.php/Working_Groups)

http://docs.opendap.org/index.php/Authentication

http://docs.opendap.org/index.php/Working_Groups


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OPeNDAP Community Working Groups Terms of Reference (abridged)

http://docs.opendap.org/index.php/Terms_of_Reference Each OPeNDAP Working Group is established to apply

members' expertise in their focus area to produce specific deliverables or outcomes

Types: Software and Documentation Minimum 3 people 6 month time-frame

http://docs.opendap.org/index.php/Terms_of_Reference


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Servers Processing Servers Aggregating Servers - OPeNDAP chains Clients Ancillary Information Services Browser Interfaces Data System Integrators (ODC)

The OPeNDAP data access protocol is used by a variety of system elements.

OPeNDAP System Elements


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Servers

Servers receive requests and provide responses via the DAP.

Servers convert the data from the form in which they are stored to the OPeNDAP data model.

Servers provide for subsetting of the data and more.


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Data Data Data Data Data Data Data

HDF5

HDF4 JDBC

FreeFormFITS

CDF CEDAR

Data

netCDF

netCDF HDF4 HDF5

Data

DSP

DSP

Data

JGOFS

Tables SQL FITS CDFFlat

Binary CEDAR

Data

General

ESML

OPeNDAP Servers


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Data

GRIBBUFR

OPeNDAP

GDS

Data

CODAR

CODAR

Data

FDS

netCDFOPeNDAP

Data

General

pyDAP

Data

DAPPER

netCDFOPeNDAP

Data

netCDFOPeNDAP

TDS

Data

General

pyDAP

Data

netCDFOPeNDAP

TDS

OPeNDAP Servers (specialized)

Data

ESG

netCDFOPeNDAP


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Servers

Servers may also provide other services

Directory traversal.

Browser-based form to build URL.

ASCII version of data.

Metadata associated with the data.

Server side functions.

http://www.bom.gov.au/bmrc/ocean/staff/gbb/AusCOM/SPINUP_FINAL/Dods/AusCOM_ECMWF_dods.htm


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Data

General

pyDAP

OPeNDAP Aggregation Servers

Data

GRIBBUFR

OPeNDAP

GDS

Data

CODAR

CODAR

Data

FDS

netCDFOPeNDAP

Data

DAPPER

netCDFOPeNDAP

Data

TDS

netCDFOPeNDAP

Data

General

JGOFS

Data

ESG

netCDFOPeNDAP


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The Aggregation Server: An Example

AggregationAggregationServerServer

File

DSP Data Set

FileFileFile

netCDF Data Set

File File

Matlab

Local

OPeNDAP

HTML, GIFMatlabClient

DSP


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Clients

Clients make requests and receive responses via the DAP.

Clients convert data from the OPeNDAP data model to the form required in the client application.


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netCDF C

Ferret GrADS

netCDF Java

IDV VisAD ncBrowse

Matlab

MatlabClient

Access ExcelIDL

IDLClient

ArcGIS

pyDAP

OPeNDAP Clients

ArcGIS

pyDAP

NCL

NCLClient


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Ancillary Information Service

• Current capability: Attributes only• Client-side only• Local and remote resources• Local resource databases

The AIS enables users to augment the metadata for a data source in a controlled way without requiring write access to the original data. By using the DAP, users are also isolated from data format issues.


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AIS enhancements

• Remote resource databases• AIS server• AIS for variables

These enhancements will greatly expand the usefulness of the AIS: Remote resource databases and an AIS server will enable third-party ‘AIS sites’ which may be sponsored by project offices or institutions, et cetera.

AIS for variables will enable adding metadata which are stored as ‘data.’


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Proposed AIS Server

Client linkedw/DAP

Software

DataSource

AISServer

AISResource

1

2

0

3

0. Client requests metadata from the AIS server (which appears no different from any other DAP server).

1. The AIS server gets metadata from data source2. The AIS server gets matching the AIS resource using the AIS database and

merges it into the metadata.3. The AIS server returns resulting the metadata object.


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OCAPI

A pure OPeNDAP C API (OCAPI) for the client-side

Applications:DAP-aware ‘commands’ for commercial

analysis programs (e.g., IDL)Scripting tools (e.g., Perl)


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ODC

IDLIDL

GrADSGrADS

FerretFerret

IDVIDV

VisADVisAD

ncBrowsencBrowse

MatlabMatlab

ExcelExcel

AccessAccess

OP

eND

AP

OP

eND

AP

GFDLnetCDF

GSFCBinary

URIHDF

GCMD

ODCODC

NVODS

- a Data System Integrator


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The DAP has been designed to be as general as possible without being constrained to a particular discipline or world view.

The Data Access Protocol (DAP)

The DAP is a discipline neutral data access protocol; it is being used in astronomy, medicine, earth science,…


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Data Access Protocol (DAP2) - Current

DAP2 currently a NASA/ESE ‘Standard’

Current server (OPeNDAP 3.x; aka SERVER3)

XML responses (implemented)

DAP3


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DAP4 - Late 2007 (?) DAP4 improvements over DAP3:

Additional datatypesSwathBlob - GIF, MPEG,…

Additional functionality Check sumModulo

The additional datatypes will enable the DAP to be used in a wider variety of circumstances and are a direct response to users’ requests.


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OPeNDAP’s Hyrax (‘Server4’)

• Uses a modular architecture to support different application-level protocols– Data access using DAP– Catalogs using THREDDS– Browsing using HTML and ASCII

• Modules for data access– Different file types– Potential for database and scripting

• Modules for commands– Commands provide varying operations for different

protocols


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Hyrax Architecture

OLFS BES

OPeNDAP Lightweight Front end Server (OLFS) Receives requests and asks the BES to fill them Uses Java Servlets Does not directly ‘touch’ data

Data

Back End Server (BES) Reads data files, Databases, et c., returns info May return DAP objects or other data


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GridFTPDAP2

GridFTPDAP2

HTTPDAP2HTTPDAP2

ASCII outputASCII output

HTML outputHTML output

Info outputInfo output

OPeNDAP Lightweight Front end ServerOPeNDAP Lightweight Front end Server

THREDDSTHREDDS

Request Formulation**Request Formulation**

Req

uest

fro

m c

lient

Res

pons

e to

clie

ntB

ESSOAP-DAP

DAP2


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BES

Network Protocol andProcess start/stopactivities

Data Store Interfaces

BES Framework

PPT*Initialization/Termination

DAP2Access

NetCDF3 HDF4 FreeForm…

DataCatalogs

Commands**BES Commands/ XML Documents

*PPT is built in (other protocols)**Some commands are built in


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Today’s Overview• DAP Servers and Services• DAP Clients and Services