Requirements Elicitation 
it has to do with the origins of the software requirements and how the software engineer can collect them.
Requirements Sources 
obtaining techniques 
This topic is designed to promote an understanding of the various sources of software requirements and the frameworks for managing them.
Goals 
Goals provide the motivation for the software, but they are often very vague. Software engineers must pay particular attention to assessing the value (relative to priority) and cost of goals.
Knowledge of the domain. 
You need to acquire or have the knowledge available about the application domain. Domain knowledge provides the context in which all the knowledge requirements elicited must be adjusted in order to understand it.
Business rules
“A student cannot enroll in next semester's courses if there are some unpaid tuition fees left” would be an example of a business rule that would be a required source for the course software
The operating environment.
time constraints on real-time performance or software constraints in an enterprise environment.
The organization's environment
the culture and internal politics of the organization. The software engineer has to be sensitive to these, as new software generally should not force unplanned change in the business process.
Rather, the software engineer obtains information from which he or she formulates requirements
Interviews
Scenarios. 
Prototypes
facilitated meetings
Observation.
Historias de usuarios
refers to short, high-level descriptions of required functionality expressed in customer terms. 
is trying to achieve a cumulative effect, whereby a group of people can bring more information about their software requirements than working individually. 
They can act in a similar way to the scenarios by Viding pro- users with a context in which they can better understand what information they need to offer. 
