When citing a source, look for the core elements, and use the ones that are relevant to your source.
Any of the core elements, except for Title of Source, may be skipped if not present.
Elements 3 - 9 should be repeated for multiple containers. (MLA 5.1)
A container is what holds the source, and it can be a journal, a book, a database, a website, etc.
Some sources may have more than 1 container. For instance, imagine an article that was originally published in a journal. The journal is the first container. It was then reprinted in a book. The book is the second container. The contents of the book were then placed in a database. The database is the third container.
Information about each container appears in the citation.