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Extending the search

The search indices

NOMAD uses elasticsearch as the underlying search engine. The respective indices are automatically populate during processing and other NOMAD operations. The indices are built from some of the archive information of each entry. These are mostly the sections metadata (ids, user metadata, other "administrative" and "internal" metadata) and results (a summary of all extracted (meta-)data). However, these sections are not indexed verbatim. What exactly and how it is indexed is determined by the metainfo and the elasticsearch metainfo extension.

The elasticsearch metainfo extension

Here is the definition of results.material.elements as an example:

class Material(MSection):
    elements = Quantity(
        description='Names of the different elements present in the structure.',
            Elasticsearch(material_type, many_all=True),

Extensions are denoted with the a_ prefix as in a_elasticsearch. Since extensions can have all kinds of values, the elasticsearch extension is rather complex and uses the Elasticsearch class.

There can be multiple values. Each Elasticsearch instance configures a different part of the index. This means that the same quantity can be indexed multiple time. For example, if you need a text- and a keyword-based search for the same data. Here is a version of the metadata.mainfile definition as another example:

    mainfile = metainfo.Quantity(
        type=str, categories=[MongoEntryMetadata, MongoSystemMetadata],
        description='The path to the mainfile from the root directory of the uploaded files',
                mapping=dict(type='text', analyzer=path_analyzer.to_dict()),
                field='path', _es_field='')

The different indices

The first (optional) argument for Elasticsearch determines where the data is indexed. There are three principle places:

  • the entry index (default, entry_type)
  • the materials index (material_type)
  • the entries within the materials index (material_entry_type)

Entry index

This is the default and is used even if another (additional) value is given. All data is put into the entry index.

Materials index

This is a separate index from the entry index and contains aggregated material information. Each document in this index represents a material. We use a hash over some material properties (elements, system type, symmetry) to define what a material is and which entries belong to which material.

Some parts of the material documents contain the material information that is always the same for all entries of this material. Examples are elements, formulas, symmetry.

Material entries

The materials index also contains entry specific information that allows to filter materials for the existence of entries with certain criteria. Examples are publish status, user metadata, used method, or property data.

Adding quantities

In principle, all quantities could be added to the index, but for convention and simplicity, only quantities defined in the sections metadata and results should be added. This means that if you want to add custom quantities from your parser, for example, you will also need to customize the results normalizer to copy or reference parsed data.

The search API

The search API does not have to change. It automatically supports all quantities with the eleasticsearch extensions. The keys that you can use in the API are the metainfo paths of the respective quantities, e.g. results.material.elements or mainfile (note that the metadata. prefix is always omitted). If there are multiple elasticsearch annotations for the same quantity, all but one define a field parameter, which is added to the quantity path, e.g. mainfile.path.

The search web interface

Comming soon ...