Origin of the plot
The classical theory of Sanskrit drama, known as Natyaśāstra makes it a rule that the plot of a Sanskrit drama 'must be famous'. Accordingly, authors of Sanskrit plays use the stories from Purāṇas, Vedic texts and classic epics, namely Mahābhārata and Rāmāyaṇa for developing plays. However, the core objective of a drama is entertainment. Since everyone is familiar with the basic plot, if the presentation of the play is not interesting or enchanting in some way, people would be bored. Hence there is emphasis on originality of the playwright. In the case of Vikramorvaśīyam, here is how Kālidāsa has adapted the original subject:Patel, G. (2014). n GujaratiVikramorvashiyamnu Mool ane Kavini Maulikata. Chapter-25, Part-2: Vikramorvashiyam in 'Mahakavi Kalidasvirachitam Malavikagnimitram, Vikramorvashiyam', Vol. 3 of Mahakavi Kalidasa-Samagra Granthavali, p. 238-240.Pandya, S. M. & Shah, U. (1993). The Sources of the Play and the Changes Brought about by Kalidasa. (Ed.s) Chapter-3, Mahakakavikalidasavirachitam Vikramorvashiyam, Saraswati Pustak Bhandar, Ahmedabad. p. 25-29. Ṛg-veda : In the 95th section, called Sūkta of the tenth cluster (called Maṇḍala), there is a dialogue between Pururava and Ūrvaśī. Situation suggests that she has left the king after living for four years with him. The king beseeches her to return, but she refuses (saying, "na vai straiṇāni santi śālavṛkānām hṛdayānyetāḥ" - meaning, the hearts of women are like those of jackals). The story ends at that. Śatapatha Brāhmaṇa: Apparently aimed at emphasizing importance of a Yagya, Pururava was attracted to Ūrvaśī when she came to his city