Data acquisition with XML : daqXML

An heterogeneous and distributed data acquisition system poses the challenge of remote operations procedures. In order for a user to perform the correct operation on a given instrument, he must know the exact configuration of the system he is accessing. Any change on the system must be communicated to the community of potential users. It is increasingly common for instrument vendors to provide a web interface for their instruments. However, each interface is proprietary and, at the moment, a standard has not yet emerged.

daqXML is a suite of software built around a standard description of instruments and measures. daqXML can be used in the design, the deployment and the operations of small to large, distributed, and heterogeneous, data acquisition systems.

Possible uses of daqXML include:

• Manage small to large monitor system (meteorological, seismic, industrial ...). Instruments added to the monitoring network automatically reconfigure the system. Data acquisition can be run at a distance. Instruments of different vendors can be seamlessly integrated.
• Create standard interfaces to instruments. For example a daqXML enabled oscilloscope sends its definition to a PC and a program in the PC creates the appropriate User Interface. The protocol , once embedded in an instrument, enables it to generate a web interface for both human access and Data Acquisition programs.
• Simplify management and usage of multiple instruments in laboratories. Users can search on the intranet the instrument they need, query the instrument to verify it's functionality and even run the measurements directly from their office.

daqXML allows the user to work in his/her favorite software environment, and then publish the procedures on an intranet or the Internet. For example :

1. A developer writes a measurement procedure on a given platform (E.G. National Instrument's Labview).
2. The developer adds the daqXML interface that has no influence on the basic functionality of the measure
3. The daqXML-enabled procedure can now register itself with a public (or restricted) registry, by publishing there a daqXML file that describes the measurement procedure, indicates the required parameters and defines the data output
4. Any daqXML client that is authorized to access the registry can retrieve the daqXML description of the measure. A client can be another labview program running on the same machine or any daqXML program, written in any language, running, on a distant workstation. The client program can automatically perform a measurement or create a User Interface for parameters configuration in order to run the desired measurement.
5. The client program sends the request to the measurement procedure
6. The measurement procedure is performed and data is transferred to the required destination

The developer does not need to bother about creating a public interface to the measurement procedure and publish it: he/she only needs to indicate to which registries the measurement description will be published. Similarly, external access to the procedure does not require any knowledge of the hardware or software functionality of the measurement. Current prototypes for example allow the exchange of information between a Labview measurement station and a web service running on PHP.

daqXML is based on XML and the procedures defined within the daqXML framework allow to :

• Describe the structure and configuration of a data acquisition system
• Define flexible, platform independent, easy to understand, scripting configurations
• Manage networked data acquisition equipment as discoverable, self describing, web services
• Provide a standardized way to exchange instructions and data within distributed data acquisition systems.

By defining a shared vocabulary that can be easily processed by humans and various types of hardware and software data acquisition applications, daqXML fosters the integration of information and process needed to conduct remote monitor and control.

The final aim of daqXML is to provide a common set of use cases, process, and vocabularies that can easily be reused and extended to allow for customized application. A subset of daqXML can be defined within a project, a company or a community.

daqXML provides an abstract description of the remote equipment, including the available set of measurements and the corresponding data structures. Such descriptions, defined as XML schemas, are available to the community that will never need to interact directly with an equipment, but only its abstraction. It is the job of the local operators to ensure that the equipment is responding to standard requests and is sending standard data following the daqXML prescriptions.