ERD for website that sells machines and lets you download a mobile app that controls them

Question

I'm creating an ERD for my graduation project creating a website that sells coffee machines and lets you download a mobile app that controls them remotely:

I will add the attributes and the relation for an entity "payment".

How can I improve this ERD?

Answer 1

We cannot judge if the entities and relationships are correct, as we don't have the requirements.

However, it is already possible to suggest improvements:

• Add the cardinalities on each relationship. For example has a Website only one Coffee Machines or several? And is a Coffee machine had by only one website or can a same machine belong to several sites? This is essential to understand the nature of the relationships but also to derive a database implementation.
• Two entities such as Coffee machine and Order shall not be directly related: a relationship is missing in-between.
• Avoid relationship names such as "Has" as much as possible. Try to be more specific. For example Website registers Membership or Customer orders Order or Website proposes Coffee machine
• The relationship between the customer and the app and the app and the machine is not fully clear. It raises more questions than it answers: do you mean that you offer a catalogue of apps to download ? Will your database contain the apps ? Or do you just want to say that the customers can download an app from the website (no need to have an entity for the latter case).