In order to combine research from multiple groups, there must be an infrastructure for sharing data and exchanging model specifications, and the information published by one group must be in a form that another group can use. The NeuroML standards are intended to facilitate data and model exchange, database creation, model publication, and also provide a common data format for communicating information among modeling-related tools.

Like the Systems Biology Markup Language, the NeuroML Standards are being developed in levels, where each level extends the features of the language.

• Level 1 provides a common data format for neuronal morphology data and metadata.
• Level 2 builds on Level 1 to include standards for describing passive membrane properties, and the dynamics of ion channels, synapses, and their distributions.
• Level 3 also includes neuronal network connectivity.
• Level 4 will include subcellular processes such as detailed calcium dynamics and signaling pathways.

Multiple schemas are used for the NeuroML standards. The links to schemas below provide readable documentation for the schema elements. All *.xsd schema files are available on the downloads page.

• Level 1 consists of a schema for metadata, Metadata_v1.6, and the main MorphML Schema, MorphML_v1.6.
• Level 2 includes information on the biophysical properties of cells (such as specific capacitance, axial resistance, and channel placement) in Biophysics_v1.6, and the properties of channel and synaptic mechanisms are described by the ChannelML schema, ChannelML_v1.6.
• Any Level 1 or Level 2 XML file will also be compliant to NeuroML_Level2_v1.6.
• Level 3 is at an early stage of development and allows specification of network connectivity. The core schema is NetworkML_v1.6.

Tools exist for converting several data formats into NeuroML. (In particular, see the website for neuroConstruct.) After a NeuroML document is generated, it can be validated against the NeuroML schemas using a web-based application, the NeuroMLValidator. The NeuroMLValidator site also provides software for translating NeuroML documents into valid code for use in simulations using GENESIS or NEURON. Detailed examples of valid documents that describe elements of published models are also available.

NeuroML is complementary to other efforts to develop markup languages:

• CellML describes cellular and subcellular level models, is built around systems of equations, and is mostly procedural rather than descriptive.
• The Systems Biology Markup Language (SBML) and NeuroML have some common applications, and future versions of NeuroML will interface with SBML.
• BrainML provides a language for neuroscience data that is centered around interoperability and exchange in the area of experimental neuroscience.

The NeuroML standards will be used extensively for model specification in neural simulators:

• GENESIS 3.0 will utilize the NeuroML standards for cell morphology, membrane properties, subcellular processes and network connectivity.
• The NEURON simulator group is also developing a representation for model specification based in part on the NeuroML standards.