1. Introduction Zachary G. Ives August 2, 2018 University of Pennsylvania
CIS 550 – Database & Information Systems
August 2, 2018
Some slide content courtesy of Susan Davidson & Raghu Ramakrishnan

2. Welcome to CIS 550, Database and Information Systems!
Instructor: Zachary Ives,
576 Levine Hall North
Office hours: Wednesdays, 3:30-4:30PM (before class)
TA: Kareem Amin,
Office hours: Tuesdays, 3:30-4:30PM, Levine N – 4th Floor Lounge
Discussion group: groups.google.com/group/cis-550-fall09
Home page:
Texts and readings:
Ramakrishnan & Gerke, Database Systems, 3rd ed.
Supplementary papers (to be handed out in class)

3. Course Format and Grading
Roughly one major topic area per week to two weeks
Readings in the text & current or influential research papers
Occasionally, summaries/commentary on papers (5%)
Homework assignment for each topic area and mini-projects (30%)
One midterm (10%), one final exam (20%)
Project (30%) – groups of 3 or 4
Build a “facebook clone”
(Or propose your own idea)
General participation, discussion, intangibles (5%)

4. What’s this Course About?
Most CS courses concentrate on code – our interest is managing and representing data
Warning: this course doesn’t focus on teaching SQL or how to be an Oracle DBA (though it will get you started)
It’s not an “application” course!
… So what in the world are we studying for 14 weeks???

5. Data – What Do We Need to Do with It?

6. Ways Information Is Represented

7. Example: An Encyclopedia Entry (www.wikipedia.com)
A database is a collection of data elements (facts) stored in a computer in a systematic way, such that a computer program can consult it to answer questions. The answers to those questions become information that can be used to make decisions that may not be made with the data elements alone. The computer program used to manage and query a database is known as a database management system (DBMS). The properties of database systems are studied in information science.
At the core of the concept of a database is the idea of a collection of generic facts, or pieces of knowledge. Facts may be structured in a number of ways, known as database models. For instance, one database model is to associate each fact with a record representing an entity (such as a person), and to arrange these entities into trees or hierarchies – the hierarchical database model. Another model is to arrange facts into sets of values which satisfy logical predicates – the relational database model.
The first database management systems were developed in the 1960s. A pioneer in the field was Charles Bachman. Two key data models arose at this time: the network model (developed by CODASYL) followed by the hierarchical model (as implemented in IMS). These were later usurped by the relational model, which was contemporary with the so-called flat model designed for very small tasks.

8. Example: To-Do List Buy school supplies due 9/4
Go to orientation on 9/4
Exercise every M/W/F
Buy Philly postcards
Take photo with Ben F.
How does this differ from the plain text model? What might you do with it that you couldn’t?

9. Example: Your PDA/Cell Phone
Calendar
Event Day When Who Where
Lunch 10/24 1pm Zack Cavanaugh’s
Advice 10/25 9am Dr. Smith 599 Levine
Biking 10/26 9am Jane Pottruck
Dinner 10/26 6PM Jane Food Court
Contacts
Who Phone Office
Zack zives 576 Levine N
Dr. Smith drsmith 599 Levine
Jane jane 2220 Walnut St.

10. What If We Want to Include Contact Info on Our Calendar?
Do we also want to keep addresses, telephone numbers etc.?
Should we expand the number of columns in our table:
Event When Who-name Who- Who-tel …. Where
Lunch 1pm Zack zives …. Cav… …
What is the trade-off in terms of entering data?

11. “Link” Calendar with Contacts?
Why can’t we “link” calendar entries with contact info, and show the results of the two?
The link could be based on something as simple as the person's name
(What’s the danger here? What else might work better?)
This brings up an issue – how to “follow links”
If we were to do this in C, how might it be done? In Java?

12. Another Kind of Link: Classes and Subclasses
Person has attributes:
ssn
PennID
set of user IDs
given name
family name …
Student IS A person who:
takes courses
is given grades
learns an academic topic
listens to lectures in class, OR over the Web, OR on videotape
This is yet another kind of information
How have you previously seen such relationships encoded?

13. Data Representation and Modeling
All of the data we’ve seen have an implicit data model
The data model includes some basic assumptions about what’s an “item” of data, how to interpret it, and so on
The relational data model was the first model that is independent of its data structures and implementation
A theory of normalization guides you in designing relations
Concepts have been adapted to form object-oriented data models, XML, etc.
There are “sibling” fields to databases with semantic models:
natural language (meanings of bags or lists of words)
information retrieval (associations between words and documents)
ontologies (inferences about relationships between classes, and classes and subclasses of relationships)
We’ll mostly focus on the relational model and its descendants

14. The DBMS Provides an Interface over the Database
A database (DB) is a large, integrated collection of data
Generally is cohesive in “some” way
A DB models a real-world organization or unit
A database management system (DBMS) is a software package designed to store and manage databases
Reliable storage & recovery of 100s of GB
Querying/updating interface and API (for applications and Web pages)
Support for many concurrent users
Why do we need a DBMS, instead of coding in Java?

15. DBMS Benefit #1: Generality and Declarativity
Don’t require the programmer or user to know details like indices, sort orders, machine speeds, disk speeds, concurrent users, etc.
Instead, the programmer/user programs with a logical model in mind
The DBMS “makes it happen” based on an understanding of relative costs of different methods

16. Benefit #2: Efficiency and Scale
Size of personal address book is probably less than 100 entries, but there are things we'd like to do quickly and efficiently:
“Give me all appointments on 10/28”
“When am I next meeting Jim?”
“Program” these as quickly as possible (and make them resilient to data format changes)
Scale to a corporate calendar with hundreds of thousands of entries

17. Benefit #3: Management of Concurrency and Reliability
Suppose other people are allowed access to your calendar and are allowed to modify it? How do we stop two people changing the file at the same time and leaving it in a physical (or logical) mess?
Suppose the system crashes while we are changing the calendar. How do we recover our work?
This requires a basic concept…

18. Transactions
Key concept for concurrency is that of a transaction: an atomic sequence of database actions (read/write) on data items (e.g. calendar entry).
Key concept for recoverability is that of a log: keeping track of all actions carried out by the db.

19. Anatomy of a Typical DBMS
(Simplification!)
API/GUI
Query
Optimizer
Stats
Physical plan
Exec. Engine
Logging, Recovery,
Schemas
Catalog
Data/etc
Requests
Index/file/rec Mgr
Data/etc
Requests
Buffer Mgr
Red = logical
Blue = physical
Pages
Pages
Storage Mgr
Data
Requests
Storage

20. The Database Abstraction Provided by the DBMS
We think of databases at two levels:
Logical structure:
What users/programmers see – program or query interface
Physical structure:
Organization on disk, indices, etc.
The logical level is further split into:
Overall database design (conceptual; seen by the DB designer)
Views that various users get to see

21. The Three-level Architecture for Databases
View 1 View 2 … View N
Schema
Logical,
Conceptual Level
Physical Level
(file organization,
indexing)

22. Data Independence
A user of a relational database system should be able to use the database without knowing about how the precisely how data is stored, e.g.
After all, you don't worry about the IEEE floating-point specs when you do division in a Java program or with a calculator
SELECT When, Where
FROM Calendar
WHERE Who = “Jane"

23. More on Data Independence
Logical data independence
Protects the user from changes in the logical structure of the data:
could reorganize the calendar “schema” without changing how we query it
Physical data independence
Protects the user from changes in the physical structure of data:
could add an index on who (or sort by when) without changing how the user would write the query, but the query would execute faster (query optimization)

24. Presentation Layer (4th Tier): Data-Driven Web Sites
HTML
view
Processing
“Data driven web sites” also add an HTML “presentation” layer on top of what we’ve seen
“Model” (data model) / “View” (query) / “Controller” (GUI)
Or they use XML plus “style sheets” to get the same effect

25. An Issue: 80% of the World’s Data is Not in a DB!
Examples:
Scientific data (large images, complex programs that analyze the data)
Personal data
WWW and (some of it is stored in something resembling a DBMS)
Data management is expanding to tackle these problems
Flexibility – data management imposes many constraints to make problems solvable
Must deal with entities outside our control
In this course, we’ll start by focusing on databases, but eventually look “outside the box” at the Web and at gluing together data from many places

26. Combining Databases with Mediators (a kind of middleware)
“Mediated Schema”
XML
A layer above the three-tiered architecture, to combine multiple databases/sources on the Web
Some of these are databases over which we have no control
Some must be accessed in special ways
We generally need to think about how to translate between different database formats
This problem of data integration is a particular focus here at Penn (and other top research universities)

27. How Does One Build a Database?
Start with a conceptual model
Design & implement schema
Write applications using DBMS and other tools
Many ways of doing this where the hard problems are taken care of by other people (DBMS, API writers, library authors, web server, etc.)
Common applications include PHP/JSP/servlet-driven web sites
The DBMS takes care of query optimization and execution

28. Conceptual Design fid PROFESSOR name Teaches Takes STUDENT COURSE sid
cid
name
semester
name

29. Designing a Schema (Set of Relations)
STUDENT
Takes
COURSE
sid
name 1
Jill 2 Bo 3
Maya
sid
cid 1 3
cid
name
sem DB
F05 AI
S05
Arch
PROFESSOR
Teaches
Convert to tables + constraints
Then need to do “physical” design: the layout on disk, indices, etc.
fid
name 1
Ives 2
Saul 8
Roth
fid
cid 1 2 8

30. Applications Use Queries in SQL
Structured Query Language, often embedded (e.g., in servlets, JSP, to some extent LINQ)
Based on restricted first-order logic expressions over relations
Not procedural – defines constraints on the output
Converted into a query plan that exploits properties; run over the data by the query optimizer and query execution engine
<html>
<body>
<!-- hypotheticalEmbeddedSQL:
SELECT * FROM STUDENT, Takes, COURSE
WHERE STUDENT.sid = Takes.sID
AND Takes.cID = cid
-->
</body>
</html>

31. Processing the Query Web Server / UI / etc STUDENT Takes COURSE
Merge
Hash
by cid
Execution
Engine
Optimizer
Storage
Subsystem
SELECT * FROM STUDENT, Takes, COURSE
WHERE STUDENT.sid = Takes.sID
AND Takes.cID = cid

32. DBMSs in the Real World A huge industry for 20% of the world’s data!
Big, mature relational databases
IBM DB2, Oracle, Microsoft SQL Server
Adding advanced features, including “native XML” support
“Middleware” above these systems
SAP, Siebel, PeopleSoft, dozens of special-purpose apps
“Application servers,” aka TP Monitors
WebSphere, WebLogic, Tomcat, …
Support transactional applications in EJB, .NET, etc.
Integration and warehousing systems
BEA AquaLogic, DB2 Information Integrator
Current trends:
Web services; XML everywhere
Smarter, self-tuning systems

33. So What about Database Research?
Not focusing on the problems of Oracle…
Understanding what’s possible to do with XML
Better query processing
Better languages for meta-info (e.g., constraints)
Better interaction with the non-database world
Data streams and sensors
Peer-to-peer architectures and data cooperatives
Integrating data from different formats
Lots of theory and systems-building
You’ll see familiar concepts in this course from operating systems and from complexity theory/logic
… And from programming languages, AI planning, …

34. In this Course...
Study relational databases, their design, how to query, what forms of indices to use.
Beyond relational algebra: a logical model of data (Datalog), recursion
XML and semi-structured data models
Understanding DB internals
How DBs are built
Performance implications
Integrating and mediating between databases (a huge problem today)

35. Your First Assignment…
Sign up to the Google group (there’s a link on the homepage)
Read the Codd paper
Write a one-paragraph summary of the key ideas in this paper and post to the discussion group