A business doesn’t necessarily own everything created by its workers. The question of ownership comes down to many factors, chief among them being the presence of an employment contract. Employees typically produce work that is owned by the business – if they write a memo at work, the business owns the copyright in that memo. However, an employment contract might modify how the employee’s work is treated, possibly by broadening or narrowing the definition of what the business owns. And it also depends on what sort of work is created, at what time, and with what resources.
Independent contractors, on the other hand, might own the work they produce themselves. This depends on a number of factors, such as whether there is an agreement between the business and the contractor, the nature of the work at issue, when the relationship began, and when an agreement was signed.
Sometimes, it isn’t even clear whether the worker is an employee or an independent contractor. Whether the business owns the property created by the worker then depends on the business’s control over the worker, the skills necessary for the job, the extent of benefits given to the worker, tax treatment of the worker, and a number of other factors.
Each situation is different and the rules or factors can’t be generalized and applied all the time. For instance, while you might think (based on the employee factors above) that all the academic work created by a university professor is owned by the university, an exception in the law vests copyright in certain works to the professor.