What are practical documents and two genres of practical documents

Two practical document genres are:1.  Documents that describe patents for new technologies and products. 2. Scientific articles that are published in scientific journals. 

A genre is a class of documents that are similar to each other. Document genres are classified according to the social role of the articles i.e. they are classified according to which context and audience the documents are intended for. Research has shown that article genres reflect the nature of research in each genre. Using genres to describe the topic and content of the documents many improve the management and the retrieval of the documents. 

1.documents that describe patents for new technology an products.
2.scientfic arcticles that are published in scientific journals.

Would this why do giraffes have long necks?