To better understand how the fourth and fifth stars work, it is important to read the Semantic Web Guide. While the first three stars give guidelines for publishing data on the Web using open document formats and under an open license, the fourth and the fifth stars introduce the concept of linked data link for reference to the Semantic Web Guide
To achieve four stars, you must do all that the previous stars advise, but in addition to using documents in an open format, the data must also be published on the web page itself using URIs to describe each piece of the data, so that anyone can point to the elements in a standardized format in the published document.
What are the benefits of
Data published following the four-star guidelines can be linked to from systems available anywhere else on the Web. Consumers can reuse parts of the data and combine it with other data.
The publisher begins to have fine control of each cell in the database and can optimize database access, load balancing, caching, and more. Other agencies that publish data can link their databases to yours using the same URI scheme.