NoSQL databases are grouped into many categories, one of them is the key-value databases. Our goal is to examine whether a system-independent key-value logical model exists. The idea came from the Redis database, which has the opaque key-value type named string, but it supports lists, hashes, sets, sorted sets, etc. If we compare them to the document databases storing JSON documents, they can have a system-independent logical model. We gathered databases said to fall into the key-value category and read their documentation considering the stored data structures. We found many subcategories under the key-value category. We found that the clean key-value databases with buckets can have a system-independent database model where the buckets collect the key-value pair, and the model is so easy. We could not identify a system-independent logical model for the rest subcategories. Additionally, we recognized some viewpoints on which the data model of the key-value databases can be examined. Altogether, considering all subcategories we cannot speak about a system-independent logical data model for key-value databases.