CS 47/147 Advanced Object-Oriented Programming - Caltech

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Book Example: File System• Files are just files. Never mindtheir structure for now.FileDir• Aside: in Unix-style filesystems, files can have manynames and be listed in manydirectories.• What are the importantcharacteristics of a directory?– Has zero or more entries, eacheither a file or directory.– Entries have names.– Has a parent, unless it’s theroot.14
Book Example: File SystemFileDir?• “parent” is a relation betweendirectories.– Formally, parent ⊆ Dir×Dir.– Draw as arrow from Dir to Dir.– “children” is its inverse:(e,d) ∈ children iff(d,e) ∈ parent.*parent (~children)• An important constraint:– For d ∈ Dir,∃ ≤ 1 e with (d,e) ∈ parent.– Indicate multiplicities on endsof arrow:? = at most 1; ! = exactly 1;+ = at least 1; * = any number15
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CS 47/147 Advanced Object-Oriented Programming - Caltech

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