# OBO: 1.3 Whiteboard

This page is intended to be a scratch pad for OBO 1.3 features and proposals.

## Contents

## Changes to Relations

The following new Typedef tags should be supported in OBO 1.3...

- transitive_under
- always_implies_inverse

**transitive_under** means that **p -transitive_under-> q** and **X -q-> Y** and **Y -p-> Z**, then **X -p-> Y**. Note that every relation is automatically transitive_over and transitive_under IS_A

**always_implies_inverse** is a boolean property. If always_implies_inverse is true for a relation **p**, it means that if **p -inverse_of-> q** and **X -p-> Y**, then **Y -q-> X**. This property could be used to define an **integral_part_of** relationship in OBO_REL, for example:

[Typedef] id: OBO_REL:part_of name: part of inverse_of: has_part [Typedef] id: OBO_REL:has_part name: has part [Typedef] id: OBO_REL:integral_part_of is_a: OBO_REL:part_of always_implies_inverse: true

Further, OBO 1.3 will allow classes to specify relationships to other terms OR to **links between other terms**. Link identifiers are specified in the following form:
```
```

```
``` **child_term_id** -*relation_id*-> **parent_term_id**

```
This new feature may not be part of the main specification, but may need to be specified in an ancillary parser extension specification (see below).
```

## General Specification Changes

The OBO 1.3 specification needs to discuss the concept of parser extensions. Parser extensions are optional addenda to the basic OBO 1.3 specification that provide additional features to the OBO language.

Parser extensions require that we add a new header tag to OBO files called **requires_extension**. The **requires_extension** tag should specify both an identifier for the required extension (so we need to figure out how we specify that) and a minimum version number for that extension.

### Extensions

There are at least two new extensions to OBO 1.3:

#### Postcomp Extension

This extension allows specially formatted post-composition expressions to be substituted for most identifier references in an OBO file. The post-composition expressions have the following format:

```
```

**genus_term_id**^*differentia_type_id*(**differentia_term_id**) [^*differentia_type_id*(**differentia_term_id**)]*

Where any of the term ids may be replaced with another post-comp expression, and parenthesis can be used in postcomp expressions to show precedence.