CS

Introduction to Database Flat File Approach Store database as CSV files use a separate file per entity, application must parse the files Challenges Data integrity implementation Durability Basic of Database Databases give access to the data while keeping the integrity of the data in a secure environment. Data Model logical structure of database data model is influenced by the structure of data D..

Basic of Networking What is Networking? Computer network is two or more devices that are connected together to share resources. Node: devices on the network Host node: servers Client: node that depends on the host node Network require network connecting devices (ex. router, switch) to connect all devices together. Network Components Server physical computer that runs software services that other..

관계 데이터 모델의 개념 기본 용어 Relation 하나의 개체에 대한 데이터를 2차원 테이블 구조로 저장한 것 Attribute 릴레이션의 열 Tuple 릴레이션의 행 Domain 하나의 속성이 가질 수 있는 모든 값의 집합 NULL 속성 값을 아직 모르거나 해당되는 값이 없음을 표현 Degree 하나의 릴레이션에서 속성의 전체 개수 Cardinality 하나의 릴레이션에서 Tuple의 전체 개수 릴레이션의 구성 Relation Schema 릴레이션의 논리적 구조 릴레이션의 이름과 릴레이션에 포함된 모든 속성 이름으로 정의 ex. 고객 (고객아이디, 고객 이름, 나이, 등급, 직업, 포인트) 정적인 특징 Relation Instance (= Relation Extension) 어느 한 시점에 릴레이션에..

Proof-of-Stake What is PoS? Proof-of-stake is an alternative to Proof-of-Work PoW might lead to a low network security with block incentives that decline over time -> miner ⬇️ PoS is one way of changing the miner's incentives for higher network security In PoS based public blockchain, a set of validators take turns proposing and voting on the next block, and the weight of each validator's vote d..

Introduction to Ethereum Ethereum is a decentralized, open-source blockchain designed to support a smart contract using Turing Complete Language for a script language ETH originally used the PoW as its consensus algorithm like Bitcoin -> it recently changed to PoS History Ethereum was conceived in 2013 by Vitalik Buterin On 30 July 2015, network went live, "Frontier", created its genesis block t..

Introduction to Lightning Network Problem of Bitcoin Bitcoin is a gossip protocol because each node must know about every single transaction that occurs globally What if just increasing the block limit? -> we need huge amount of storage This will result extreme centralization of Bitcoin nodes and miners to the only oes who could afford this processing Having privileged, trusted parties will caus..

Delay, Loss, Throughput in Networks Delay in networks Packets queue in router buffers When packet arrival rate to link (temporarily) > output link capacity -> packets queue, wait for turn d = $d_{proc}$ + $d_{queue}$ + $d_{trans}$ + $d_{prop}$ -> 한 라우터를 거쳐갈 때마다 $d_{proc}$: processing delay, determine output link by forwarding table lookup, 무시해도 되는 정도 $d_{queue}$: queueing delay, tme waiting at o..

Bitcoin Transaction Transaction Transaction is references previous transaction outputs as new transaction inputs and dedicates all input Bitcoin values to new outputs (input money == output money) Transactions are not encrypted Standard tx outputs nominate address, and the redemption of any future inputs requires a relevant signature in Bitcoin transaction, if money left, must spend it to myself..

Symmetric Key Cryptography Cyptographic Hash Functions Cyrptographic Hash Functions are used to guarantee the integrity of data. Cytographic Hash Function H stasfies the following properties: Message Digest Preimage Resistant: it must be one way Collision Resistant It's often used as a component of other cryptography algorithms used to compress a large data to a smaller one used to generate a de..

HashCash Hashcash CPU cost-function computes a token which can be used as a proof-of-work. Cost-functions Cost-function should be efficiently verifiable, but parameterisably expensive to copute MINT() Client must compute a token(denoted T) using a cost-function MINT() which is used to create tokens to participate in a protocol with a server VALUE() Server will check the value of the token using ..