According to the International Organization for Standardization (ISO), a standard is a document that provides requirements, specifications, guidelines or characteristics that can be used consistently to ensure that materials, products, processes and services are fit for their purpose.
Standards are generally identified by standard reference numbers, which have 2 components:
The standards reference number usually gives an indication of adoption where standards are equivalent.
Let's look at an example: UNI EN ISO 9001
The three standards, ISO 9001, EN ISO 9001 and UNI EN ISO 9001 are identical other than the reference numbers.
Question: The library does not have Italian Standards. What if you need UNI EN ISO 9001?
NUS Libraries has a good set of British Standards (We subscribe to British Standards Online). Since the British has also adopted ISO 9001, you can search for the version that is adopted by the British (i.e. BS EN ISO 9001) since the content is identical to UNI EN ISO 9001.