I'm reviewing the UniProt data model and I'm confused by what is a protein. Originally, I thought that a protein was defined by its sequence of amino acids. However, the fact that isoforms of a gene are stored in one entry for UniProt/Swiss-Prot leads me to believe a protein is defined by the gene from which it originates. Otherwise, these alternative splicing would receive distinct UniProt/Swiss-Prot entries. Or perhaps it is more complicated than that and if isoforms are distinctly different enough they receive different entries? Just confused a bit by the definition of protein in this light. 

Looking at the word itself, iso- means equal and isoform would seem to mean equal form. Understanding that structure is more conserved than sequences I would understand that form is better to define a protein than sequence. But I don't think this is what isoform really means from looking at the data. 

Any help appreciated.  
https://ghr.nlm.nih.gov/primer/howgeneswork/protein

Protein is a molecule made of amino acids that have a specific function. Sometimes changes in protein sequence due to alternative splicing are very little and have almost no effect on function in other cases differences in sequence and function are dramatic. So one gene can encode multiple isoforms of the same protein and/or multiple different proteins.