The data will certainly belong to the company. As Bednobs says, they may well own the software as well. Even if you designed it in your own time, without payment, if it is related to your job then it is likely that the company can claim rights to it, unless your contract specifically says you are entitled to rights in work done outside company time. If you designed the software before you worked for the company, then you have a strong claim to the rights for yourself. As a general rule, you can only claim rights if you have a specific agreement with your employers, or if the work done is not related to your job. You would have to discuss this with them or consult a firm of Intellectual Property Attorneys if you feel that you should own the rights.