From 6bf4b90c90f15f4ab60833bddf5b5756d1a6b1f6 Mon Sep 17 00:00:00 2001
From: Elizabeth Alexander Hunt <me@liz.coffee>
Date: Thu, 2 Jul 2026 11:55:17 -0700
Subject: Init

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+#+TITLE: Purpose of database systems
+
+* Issues with Filesystem vs Database
+** Redundancy
+In two different departments, might keep the same data unnecessarily.
+
+** Inconsistency
+Data in one place might change, but does not automatically change elsewhere.
+
+* Purpose of DB systems
+** Data isolation - multiple files and formats
+How data is stored is not important to the DB user
+
+** Integrity problems
+Keeping all data within some requirements (e.g. 0 <= GPA <= 4.0)
+
+** Atomiciticy of updates
+All updates should be all or nothing:
+  + Giving friend $100
+    READ A; A -= 100; UPDATE A;
+    READ B; B += 100; UPDATE B;
+    - If fails before B updated but A is updated, should roll back
+
+** Concurrent access
+Correct order of execution on each piece of data - filesystem won't protect against 
+
+** Security problems
+Some DB users should only be able to access global/their own data - filesystem shows entire file
+
+* History
+** Earliest systems were sheets of paper kept in wooden file cabinets
+** They were trying to make it right since 60's
+*** Hierarchial Model - IBM (~1968)
+Used Trees with parent-child nodes
+            USU
+          /     \
+       Jane      Dave
+      /          /   \
+  CS5800     CS5800  CS5050 
+
+Issue: Cannot have a common parent. To find which students take a single course, must iterate over all.
+       Cannot have many-to-many relationships
+
+*** Network Model - General Electric
+Used Graphs
+            USU
+          /     \
+        Jane     Dave
+           \     /  \
+           CS5800    CS5050 
+
+Issue: Still uses pointers (difficult, need to know exactly where address is)
+       Still cannot have a node without a parent - cannot have a course without students
+
+*** Relational - IBM (Codd's Model) (~70's)
+The issue with both Network & Hierarchial is they still use "linked lists".
+
++ Provided mathematical foundation for Relational DB's
++ Big Abstraction win: Seperated physical storage of data from its conceptual representation (no pointers!)
++ Introduced high level query language
+
+*** GIS (~80's)
+*** 90's
+Multimedia databases, real-time-databases, xml, NOSQL database
+
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