# Limitations

## Implementation Limitations

The following are limitations in the current SDO implementation:

1. There is no support for multi-byte character sets. This will be considered, depending on community requirements, in a Unicode-enabled version of PHP.

## SDO Limitations

The following SDO 2.0 concepts are not supported in the current PHP implementation. It is not necessarily the case that these will all be added over time. Their inclusion will depend on community requirements.

1. Bi-directional relationships.

2. Type and property alias names.

3. Read-only properties.

4. The Helper classes defined in SDO 2.0 are not directly implemented. However equivalent function is provided in a more natural way for PHP. For example the function of `CopyHelper::copy()` is provided by applying the PHP clone keyword to a data object.