(b) (3) (a) (4) (a) (5) Further processing for archiving purposes in the public interest, scientific or historical research purposes or statistical purposes may be considered compatible with those purposes, subject to appropriate safeguards. Data Minimisation Personal data undergoing processing must be adequate, relevant and not excessive in relation to the purposes for which they are processed. This requirement shall not only refer to the quantity but also the quality of personal data. Accuracy Personal data undergoing processing shall be accurate and, to the extent necessary, must be kept up to date. Storage Limitation (a) Personal data undergoing processing shall be preserved in a form which permits identification of data subjects for no longer than is necessary for the purposes for which those data are processed. (b) Personal data must be deleted once the purpose for which it was processed has been achieved or must only be kept in a form that prevents any direct or indirect identification of the data subject. 4. Lawfulness of processing (1) The processing of personal data shall be proportionate and appropriate in relation to the purpose or purposes pursued, taking into account the interests, rights and freedoms of data subjects, and shall be considered lawful only if it meets at least one of the following bases: (a) the data subject gives his or her consent to a specified purpose, subject to the conditions of consent set out in Section 5; (b) the processing is necessary for entering into or for the fulfilment of a contract to which the data subject is a party; (c) the processing is necessary for compliance with a legal obligation to which the controller is subject; (d) the processing is necessary to protect the vital interests of the data subject or another person; (e) the processing is necessary for the legitimate interests of the controller or a third party, except where such interests may prejudice or harm the interests, rights and freedoms of data subjects and that override those of the controller or third-party; (f) the processing is necessary for the performance of a task carried out in the public interest or in the exercise of official authority vested in the controller; or (g) the processing is carried out for archiving purposes in the public interest, or for scientific or historical research purposes or statistical purposes, subject to appropriate safeguards for the rights and freedoms of data subjects. 6