A Blockchain is nothing more than a database. Blockchain offers many advantages as compared to other databases. It has a decentralized structure with no single point of failure and the data stored on the Blockchain is completely tamper proof.

1. Types of Blockchain – Public, Private and Permissioned
There isa greatinterestinBlockchainnowadays.AsBlockchain –the underlyingtechnologybehind
Bitcoin– has slowlystartedgainingpopularity,organisationsacrossthe worldhave started
expressingtheirdesirestohave aBlockchainbaseddatabase systemfortheirdailyoperations.
A Blockchainisnothingmore thana database.Blockchainoffersmanyadvantagesascomparedto
otherdatabases.Ithas a decentralisedstructure withnosingle pointof failure andthe datastored
on the Blockchainiscompletelytamperproof.Also,dataonce storedona Blockchainwill alwaysbe
storedthere andall the detailsof transferandstorage are visible toeveryone connectedtothe
networkandto anyone notconnectedtothe networkwhowishestoverifysuchdetails.
PublicBlockchain
In a PublicBlockchain,anyone canreadandwrite the data storedon the Blockchainasit is
accessible toeveryoneinthe world.A personcanbecome a memberof the Blockchainnetworkand
can store,sendand receive dataafterdownloadingthe requiredsoftware onhisdevice.
A PublicBlockchainiscompletelydecentralisedasthe permissionstoreadand write dataontothe
Blockchainare sharedequallybyall the connectedusers,whocome toa consensusbefore anydata
isstoredon the database.A PublicBlockchainisbasedonacompletelytrust-lesssystemwhere no
useris givenspecial privilegesonanydecision.
The most commonimplementationsof aPublicBlockchainare BitcoinandEthereumwhere the
publicnature of Blockchainallows usersfromvariousbackgroundstocome ona commonplatform
for makingtransactionsandeliminatesthe needforthirdpartyvendorsbymakingtransactions
directbetweenusers.
As itis decentralised,aPublicBlockchainisalsomathematicallyveryhard tohack as the cost of
hackingbecomestoohighfora systemwhere everynodeconnectedissyncedwith the entire
Blockchaindatabase andmore importantly,once ahack isdiscovered,the value of the hackedcoins
woulddiminishexponentially –thusincurringhuge lossesonthe hacker(he hadto investa lotof
hardware to overtake the networkhashrate)
Since all transactionsina publicBlockchainneedtobe verifiedbythousandsof users,the
transactionverificationprocesscanbecome verytime consuming. The userspaya largeramountof
transactionfee here ascomparedto the Private andPermissionedBlockchain.
Private Blockchain
In a PublicBlockchain,here the permissionstowrite dataontothe Blockchainare controlledbyone
organisationwhichishighlytrustedbythe otherusers.Thisorganisationmay/maynotallow usersto
have access toread the data, as publicreadabilitymightnotbe necessaryinmostcases.Insome
situations,the organisationmightwantthe publictoauditthe data.Limited/restrictedread
permissionsalsoprovide agreaterlevelof privacytothe users,a feature notavailable inPublic
Blockchains.
The organisationincontrol hasthe powertochange the rulesof a Private Blockchainandmayalso
decline transactionsbasedontheirestablishedrulesandregulations.
In a Private Blockchain,the transactionsare quickerastheycanbe verifiedbe asmall numberof
devices.Thus,the userspaylesseramountsof transactionfeessince the numberof people verifying
the transactionisfewerthanin a PublicBlockchain.

2. Also,the devicesare verywell connectedandanyfaultscanbe fixedbyhumanintervention,which
can be easilyapprovedbythe userssince the userstrustthe single organisationincontrol of the
Blockchain.
PermissionedBlockchain
A PermissionedBlockchainisatype of Private Blockchainandsharesmanyfeaturesof the latter.A
PermissionedBlockchainprovidesahybridbetweenthe ‘low-trust’providedbyPublicBlockchains
and the ‘single highly-trustedentity’modelof Private Blockchains.PopularlycalledaConsortium
Blockchain,itisone where insteadof allowinganypersonwithaninternetconnectiontoparticipate
inthe verificationof the transaction processorallowingasingle companytohave full control,afew
selectednodesare predetermined.
For example –imagine aconsortiumof 10 companies,eachof whichoperatesadevice connectedto
the Blockchainnetwork.If company‘2’onlytradesand sharesitsinvoiceswith‘3’,‘4’and ‘5’ there is
no needforthe othercompaniestobe giventhe permissionstoreadthe shareddata.
Althoughsome degree of decentralisationismaintainedintheirstructure,the participantshave the
powerto grant read/write permissionstootherparticipants,leadingtothe ‘PartiallyDecentralised’
designof PermissionedBlockchains.
The transactionsare quickto verifyinaPermissionedBlockchain asthere are a handful of verifiers,
withthe transactionfee miniscule thusincreasingthe overallefficiencyof transactions.Like Private
Blockchains,the PermissionedBlockchainsmaintainthe privacyof auser’sdata,without
consolidatingpowerwitha single organisation.
WhichBlockchain is the bestfor you?
There isno Blockchainthatcan be recommendedtoeveryone.Eachtype has itspros andcons. The
mainconcernssurroundingPublicBlockchainsare privacyandscalability.Bothcanbe mitigatedto
some extentbutare not completelysolvedatpresent.
Similarly,Private Blockchainshave asingle pointof failure andbringingvariousorganisationstouse
a commonmodel remainsaconcern.
Both the modelsare neededinvariousindustriesandconstant developmentsare beingdone on
boththe PublicandPrivate models.So,whichmodel thatwouldsuityouthe best?Well,thatclearly
dependsonthe type of data beingstored,andwhoall will needthe accesstoreadand write data on
the Blockchainandwhetherall these participantsneedtobe givensame ordifferentprivilegesof
readingandwritingonthe database in concern.