With their user-centric approach and iterative development process, agile software development (ASD) methods, including the widely used Scrum framework, have revolutionised the industry. The use of user stories, brief representations of stakeholder requirements, is essential to the ASD field. However, the lack of a standardised method for expressing user stories presents difficulties for agile practitioners working with end users. This thesis proposes the creation of a domain-specific modelling language (DSML) built on an ontology to create a visual standard for user stories to address the challenge mentioned above. This research aims to add to the body of knowledge regarding ASD by offering a valuable and simple method, especially for Product Owners (POs) and agile practitioners who work in this area. This work successfully addresses several issues related to stakeholder collaboration, ambiguity reduction, and knowledge storage by implementing the DSML, the User Story Modelling Language & Notation (USMN), within the Agile and Ontology-Aided Modelling Environment (AOAME), which stores modelling elements in a knowledge graph. The USMN is developed in this thesis using a Design Science Research methodology to create user stories that are both machine- and human-interpretable.