A key issue in Mosaic's case against Dunnes is whether the UK group's designs are original, which makes it illegal to copy them.
Mosaic says the clothes over which it is suing the Irish chain are based on original "unregistered designs", and are therefore protected by the Republic's laws. As result, it was illegal for Dunnes to copy and sell clothes based on them.
Following an EU directive, unregistered designs have been protected under Irish law since 2003. This is the first Irish case to deal with the issue.
Brussels created the unregistered design idea for products such as designer clothing, as they have a short shelf life and do not benefit from the longer-term protection offered by trademarks and patents. But products do not qualify if they are not original designs.
Mosaic's senior counsel, Michael McDowell, explained that in order to qualify, unregistered designs must have individual character and must be new. In other words, they cannot be identical to something that has been available before.
He added that they must make an "overall impression on the informed user of being different from products based on designs that were previously available".
Mr McDowell said that in this case, the "informed user" would be a "female purchaser of the products with a keen sense of fashion and a knowledge of the design and the outlets involved".