The bdg-formats schemas¶
The schemas that comprise ADAM’s narrow waist are defined in the bdg-formats project, using the Apache Avro schema description language. This schema definition language automatically generates implementations of this schema for multiple common languages, including Java, C, C++, and Python. bdg-formats contains several core schemas:
- The Alignment schema represents a genomic read, along with that read’s alignment to a reference genome, if available.
- The Feature schema represents a generic genomic feature. This record can be used to tag a region of the genome with an annotation, such as coverage observed over that region, or the coordinates of an exon.
- The Fragment schema represents a set of read alignments that came from a single sequenced fragment.
- The Genotype schema represents a genotype call, along with annotations about the quality/read support of the called genotype.
- The Sequence and Slice schema represents sequences and slices of sequences, respectfully.
- The Variant schema represents a sequence variant, along with statistics about that variant’s support across a group of samples, and annotations about the effect of the variant.
The bdg-formats schemas are designed so that common fields are easy to query, while maintaining extensibility and the ability to interoperate with common genomics file formats. Where necessary, the bdg-formats schemas are nested, which allows for the description of complex nested features and groupings (such as the Fragment record, which groups together Alignments). All fields in the bdg-formats schemas are nullable, and the schemas themselves do not contain invariants around valid values for a field. Instead, we validate data on ingress and egress to/from a conventional genomic file format. This allows users to take advantage of features such as field projection, which can improve the performance of queries like flagstat by an order of magnitude.