Mike Carey Information Systems Group Computer Science Department UC Irvine.
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Transcript of Mike Carey Information Systems Group Computer Science Department UC Irvine.
Database Systems:
A Vertical Slice of Computer Science … or …
It’s All About the Data!
Mike CareyInformation Systems GroupComputer Science DepartmentUC Irvine
©2003 BEA Systems, Inc. | 2
Wait … Who Is This Guy?
Carnegie-Mellon University, 1975-80 B.S. and M.S. Student, EE/ECE
UC Berkeley, 1980-83 Ph.D. Student, CS
University of Wisconsin, 1983-95 Assistant/Associate/Full Professor, CS
IBM, 1995-2000 Industrial Researcher & Software R&D Manager
Propel Software, 2000-01 Startup Company Fellow/CTO/VP of Software
BEA Systems, Inc., 2001-08 (acquired by Oracle) Industrial Software Architect & Sr. Engineering
Director And now I’m here…
Trivia tidbit:Here’s a photo of my first (ever) CS TA
Plan For Today’s Talk
Okay, so just what is a database system? Based on lecture notes from the UW-Madison
database curriculum, as immortalized in Database Management Systems (Ramakrishnan & Gehrke, a.k.a.“the Cow book”)
The database field is a vertical slice of all of CS! You’ll see what I mean (and why)…
What’s exciting in “database systems” today? UCI Information Systems Group (ISG) and
beyond!
What is a Database System?
So what’s a database? A very large, integrated collection of data
Usually a model of a real-world enterprise or a history of real-world events
Entities (e.g., students, courses, Facebook users, …)
Relationships (e.g., Susan is taking CS 234, Susan is a friend of Lynn, Mike filed a grade change for Lynn, …)
What’s a database management system (DBMS)? A software system designed to store, manage,
and provide access to one or more such databases
Evolution of DBMS
Files
CODASYL/IMS
Relational
Manual Coding
Byte streams
Majority of application development effort goes towards building and then maintaining data access logic
Relational DB Systems
Declarative approachTables + views bring “data independence”Details left to system
Designed to simplify data-centric application development
Early DBMS Technologies
Records and pointers
Large, carefully tuned data access programs that have dependencies on physical access paths, indexes, etc.
New Data
???
…
…
New Data
???
…
…
New Data
???
…
…
Why Use a DBMS?
Data independence
Efficient (and automatic) data access
Reduced application development time
Data integrity and security
Uniform data administration
Concurrent access and recovery from crashes
Why Study Databases?
Shift from computation to information At the “low end”: explosion of the web
(a mess!) At the “high end”: scientific applications
Datasets increasing in diversity and volume Digital libraries, interactive video, social
media, genomic data, big science data, …
... need for DBMS exploding! DBMS field encompasses most of CS
OS, languages, theory, AI, multimedia, logic, …
?!
Data Models
A data model is a collection of concepts for describing data (to one another or to a DBMS)
A schema is a description of a particular collection of data, using a given data model
The relational model is the most widely used data model today
Relation – basically a table with rows and (named) columns
Schema – describes the tables and their columns
Levels of Abstraction
Many views of one conceptual (logical) schema and an underlying physical schema
Views describe how different users or groups see the data
Conceptual schema defines the logical structure of the database
Physical schema describes the files and indexes used “under the covers”
Physical Schema
Conceptual Schema
View 1 View 2 View 3
Bits
On-Disk Data
Structures
Logical Model
Lies!
Example: University DB
Conceptual schema: Students(sid: string, name: string, login: string,
age: integer, gpa: real) Courses(cid: string, cname: string, credits:
integer) Enrolled(sid: string, cid: string, grade: string)
Physical schema: Relations each stored as unordered files Have indexes on first and third columns of Students
External schema (a.k.a. view):
CourseInfo(cid: string, cname: string, enrollment: integer)
Data Independence
Applications are insulated from how data is actually structured and stored!
Logical data independence: Protection from changes in the logical structure of data
Physical data independence: Protection from changes in the physical structure of data
One of the most important benefits of using a DBMS! Allows changes to be made w/o application
rewrites
Example: University DB (cont.)
User query (in SQL, against the external schema): SELECT c.cid, c.enrollment FROM CourseInfo c
WHERE c.cname = ‘Computer Game Design’
Equivalent query (against the conceptual schema): SELECT e.cid, count(e.*) FROM Enrolled e, Courses c
WHERE e.cid = c.cid AND c.cname = ‘Computer Game Design’
GROUP BY c.cid
Under the hood (against the physical schema) Access Courses – use index on cname to find associated
cid Access Enrolled – use index on cid to count the
enrollments
Architecture of a DBMS
A typical DBMS has a layered architecture
The figure doesn’t show the concurrency control and recovery components
This is one of several possible architectures; each actual system has its own variations
Query Optimizationand Execution
Relational Operators
Files and Access Methods
Buffer Management
Disk Space Management
DB
Note:These layersmust considerconcurrencycontrol and
recovery
Queries
DB Field is a Vertical Slice of CS “I like programming languages and
compilers” Consider high-level, declarative languages like
SQL “I like low-level operating systems issues”
DBMSs manage records, memory, locks, logs, … “I really want to work on distributed
systems” Distributed and parallel database systems are
ripe with distributed algorithms and systems issues (!)
“Data structure and algorithm design is really cool” Database indexes are data structures on disk (or
flash)
(And so on!)
What’s Exciting in DB Land Today? The Web is full of database challenges
(“Big Data”!) A box for keywords only goes so far…
▪ How can I query the web, e.g., “Find me 5-string Fender bass guitars for sale in the $1000-1500 price range”
Click streams and social networks generate lots of data▪ How can I query and analyze all that data (e.g., to act
on it)? Ubiquitous computing is data-rich, too
Build, deploy, and use location-based data services
Query and aggregate streams of sensor or video data
There’s data everywhere, and of all shapes and sizes How do we integrate it, e.g., for rapid crisis
response? And when we do, how do we ensure
privacy/security?
Ex: DB Challenges at Facebook Data store for low-latency, high-traffic Web
sites Only have a few hundred milliseconds to generate an
entire page Data heavily cached outside the DBMS today, which is
“far from ideal” Data systems for offline/batch-oriented
processing I mentioned this before: clickstream analysis, graph
analysis, etc. Potentially interested in faster, approximate answers Would like to do this in real time as well, as data arrives
Hardware trends (always) present new opportunities Flash storage, for example Multicore CPUs (nobody uses them very well yet)
Cool open source work at Facebook related to DBs Hive: Open source SQL on top of Hadoop Cassandra: Large-scale distributed storage for
semistructured data
AsterixDB System (From UCI)(http://asterixdb.ics.uci.edu/)
Disk
MainMemory
Disk
CPU(s)
ADMData
MainMemory
Disk
CPU(s)
ADMData
ADMData
Hi-Speed Interconnect
Data loads & feeds from external sources (XML,
JSON, …)
AQL queries & scripting
requests and programs
Data publishing to
external sources and
apps
ASTERIX Goal: To ingest, digest, persist, index, manage, query, analyze, and publish massive quantities of semi-structured information…
(ADM = ASTERIX Data Model, AQL
= ASTERIX Query
Language)
MainMemory
CPU(s)
17
Summary
A DBMS is for storing and querying big datasets
Benefits of using a DBMS are many: enables rapid development of new applications (“what, not how”), recovers after crashes, supports (safe) concurrent access, helps maintain data integrity and security, …
Levels of schema abstraction data independence
DB research is a vertical slice of all of CS (“for data”)
Big Data experts are in high industrial demand! ()
Data is what it’s all about today! So, consider taking our three classes: CS 122A/B/C.