the obvious object is the note objectless obvious one is notebook container object tags and dates also seem to be objectsbut we can use dates from python' standard library and comma-separated string for tags to avoid complexityin the prototypelet' not define separate classes for these objects note objects have attributes for memo itselftagsand creation_date each note will also need unique integer id so that users can select them in menu interface notes could have method to modify note content and another for tagsor we could just let the notebook access those attributes directly to make searching easierwe should put match method on the note object this method will accept string and can tell us if note matches the string without accessing the attributes directly this wayif we want to modify the search parameters (to search tags instead of note contentsfor exampleor to make the search case-insensitive)we only have to do it in one place the notebook object obviously has the list of notes as an attribute it will also need search method that returns list of filtered notes but how do we interact with these objectswe've specified command-line appwhich can mean either that we run the program with different options to add or edit commandsor we have some kind of menu that allows us to pick different things to do to the notebook we should try to design it such that either interface is supported and future interfacessuch as gui toolkit or web-based interfacecould be added in the future as design decisionwe'll implement the menu interface nowbut will keep the command-line options version in mind to ensure we design our notebook class with extensibility in mind if we have two command-line interfaceseach interacting with the notebook objectthen notebook will need some methods for those interfaces to interact with we need to be able to add new noteand modify an existing note by idin addition to the search method we've already discussed the interfaces will also need to be able to list all notesbut they can do that by accessing the notes list attribute directly we may be missing few detailsbut that gives us really good overview of the code we need to write we can summarize all this in simple class diagram