Both the Attributes of the Logical model and the Columns of the Relational model allow for extending the default information related to these objects through "User Defined Properties".
You can define these properties by right-clicking on the design in the browser, selecting "Properties" and then "User Defined Properties".
Click the green PLUS to create a new property library.
Here you can create new properties and of a specific type that can be associated with Attributes, Columns or whatever.
You can access these properties in the standard Property Edit windows
Hope this helps
Thank you for pointing out that I used the word ARROW, when I meant to say PLUS.
As FC60 described with images that I should have included myself, at the top level in the browser is the DESIGN object. Below this are the models that belong to that design.
User properties are defined at the Design level, and applied to Entities within the design.
It appears that you were working within the Entity itself.
Also, if you would like assistance, posting larger images helps us help you.