DAS 1.6 Changes
Although it is the first in several years, the DAS 1.6 specification is not principally intended to accommodate brand new features. Instead, it broadly aims to:
- correct inconsistencies and ambiguities in the DAS 1.53 specification
- ratify concepts and extensions from DAS 1.53E that are already in widespread use
- make more areas of the protocol easier to implement by relaxing unnecessary or unfeasible requirements
- deprecate legacy or little used elements of the protocol
As a result the changes are largely non-destructive and compatible. The major exception to the above is the introduction of "parent/part" hierarchical features. This is a replacement for the <GROUP> element, inspired by DAS/2 rather than 1.53E.
From the specification itself, the list of changes includes:
- Introduced the concept of "coordinate systems" and the DAS Registry.
- New commands: sources and structure. These commands are taken from DAS 1.53E, with some changes.
- Added support for using ontologies in annotations.
- Deprecated commands: dsn, dna and link.
- Stylesheets now support histograms, colour gradients and line plots, more colours, and are better characterised. The "toomany" glyph is deprecated.
- Entry points command gained "paging", and other minor changes.
- Nonpositional annotations are now supported.
- Features command gained "maxbins".
- All command responses are now described by RELAX NG schemas.
- Relaxed the constraints on data source names.
- Clarified the use of HTTP and DAS status codes.
- Clarified content encodings and compression.
- Added requirement for clients to include specific request headers.
- Features command gained hierarchical referencing, in favour of groups.
- Segment query parameters no longer require start and end positions.
- Several elements in the features command response are now optional.
- Unified the format of segment XML across all commands.
- Clarified the content of attributes across several commands, such as segment versions.