Dates on the client-side are formatted in the ISO format (2018-01-01), JSON date format, and are saved on the data base in that format. On the server side the dates can have many different formats, configured by the server administrator.
Server side
OutSystems use the yyyy-MM-dd date format to store dates in the data base. Is possible to choose the format that inputs accept when entering this type of data. In the grid is expected to use that same configuration to format the columns of type date which can be changed on the Service Center:
On the client-side the date to display is formatted using the date format options from Service Center, and the grid will store and present dates in that format. However, the format handled to then save to the data base is the yyyy-MM-dd format. So, every time we change a cell of type date, we'll store the value on the grid side in one of the possible formats of Service Center, then on save the data, the date attributes will be converted to the same format as the data base format, which is standard, and sent to the server.