Remove duplicate content in DB2 lesson1 and lesson2

Data Bases 2/lesson_01.md

@@ -1,8 +1,8 @@
 # DB2 - lesson 01
 #### Paraboschi
 ##### 6 October 2015
-### 1. Transaction Model
-#### Transaction Properties and Mechanisms
+## Transactional Systems
+### Transaction Properties and Mechanisms
 - ##### Atomicity
     - Abort-rollback-restart
     - Commit protocols
@@ -13,69 +13,10 @@
 - ##### Durability
     - Recovery management
 
-#### Corresponding modules
+### Corresponding modules
 - ##### Atomicity and Durability
     - Reliability Manager
 - ##### Isolation
     - Concurrency Control System
 - ##### Consistency
     - Integrity Control System at query execution time (with DDL Compilers support)
--------
-### 2. Concurrency
-#### Advantages of Concurrency
-
-Modern computers are capable of executing different processes in a concurrent way,
-Concurrency is also important in DBMS because it allows multiple Transactions at the same time
-
-ex: Two students enroll contemporarily on the Politecnico site.
-
-Concurrency is made by
-- time sharing on a single processor
-- or sharing the processes on multiple CPU cores.
-
-#### Concurrenct executions
-A problem may rise when we heve two or more concurrent operations modifying the same data.
-
-There are several ways of managing the problem:
-
-- ##### Serial executions
-The two operations are queued and executed separately in time.
-- ##### Interleaved execution
-
-- ##### Nested execution
-###Concurrency Problems
-####Lost update
-```
-T1: R(D,V1)
-V1 = V1 + 3
-T2: R(D,V2)
-V2 = V2 + 6
-T1: W(V1,D)     D=103
-T2: W(V2,D)     D=106!
-```
-####Dirty read
-```
-T1: R(X,V1)
-T1: V1 = V1+3
-T1: W(V1,X)     D=103
-T2:R(X,V2)
-T1: ROLLBACK
-T2: V2 = V2+6
-T2: W(V2,D)     D=109
-```
-####Non-repeatable read
-```
-T1: R(D,V1)
-T2: R(D,V2)
-T2: V2 = V2 + 6
-T2: W(V2,D)      D=106
-T1: R(D,V3)     V3<>V1!
-```
-####Ghost update
-```
-T1: R(D,V1)
-T2: R(D,V2)
-T2: V2 = V2 + 6
-T2: W(V2,D)      D=106
-T1: R(D,V3)     V3<>V1!
-```

Data Bases 2/lesson_02.md

@@ -2,11 +2,26 @@
 #### Paraboschi
 ##### 12 October 2015
 ## Concurrency Control
+
+### Advantages of Concurrency
+
+Modern computers are capable of executing different processes in a concurrent way,
+Concurrency is also important in DBMS because it allows multiple Transactions at the same time
+
+ex: Two students enroll contemporarily on the Politecnico site.
+
+Concurrency is made by
+- time sharing on a single processor
+- or sharing the processes on multiple CPU cores.
+
+### Concurrenct executions
+A problem may rise when we heve two or more concurrent operations modifying the same data.
+
 Tens, hundredss, thousands of transactions per second cannot be executed serially
 
 Concurrency need to be controlled to avoid anomalies.
 
-### Concurrent executions
+### Types of concurrency
 b(Tx) = begin transaction x  
 e(Tx) = end transaction x
 - __serial__ b(T1) e(T1) b(T2) e(T2)  

README.md

@@ -10,6 +10,6 @@ The idea is the following:
 Subject|completed to|last lesson
 ---|---|---
 Artificial Intelligence | lesson 4|lesson 4
-Data Bases 2|review needed|lesson 2
+Data Bases 2|lesson 2|lesson 2
 Formal Languages and Compilers| lesson 3 | lesson 5
 Software Engineering 2 | missing content| lesson 4