According to the principle of proportionality (s. Art. 6 para. 2 FDPA), only data that is necessary and appropriate for the specific, communicated purpose may be collected. For example, when an e-book is ordered online, the provider only needs the name (identification), possibly the date of birth (identification, contractual capacity), an e-mail address (communication) and credit card details (payment). Information about a physical address is in this case neither necessary nor appropriate for the transaction. In 2018, the Federal Data Protection and Information Commissioner (FDPIC) found that the sporting goods retailer Decathlon required customers to provide an email address or telephone number when making purchases in its Swiss stores (FDPIC, Activity Report 2018/2019). Decathlon subsequently stated that data collection would be voluntary in future and revised its customer information accordingly (FDPIC, Activity Report 2019/2020). The principle of proportionality also stipulates that data may only be stored for as long as is necessary for the purpose. Since there is usually sufficient storage capacity and therefore no technical necessity for deletion, failure to delete data as required is possibly one of the most common violations of data protection law.