E-learning systems should deliver contents which reflect various phenomena of the language as it is used. E-learning systems that would include real-world Korean expressions such as those in web documents, mobile text messages, or twitter posts, would be useful for learners. The linguistic characteristics of these informal documents are quite different from those of formal documents such as academic text books or online newspaper articles. That is why many Korean learners have trouble in understanding these documents. We need to develop a systematic device to treat them in an e-learning system. In this paper, we construct two types of corpora: one is made of formal documents like online news articles; the other is made of informal documents like customer reviews about new products in web blogs. By comparing these corpora, we show how expressions differ in these two types of corpora. We survey the main characteristics of the informal corpus. Given that a significant proportion of text is informal, we propose Local Grammar Graphs (LGG) as an appropriate model to treat them effectively in Korean e-learning systems.