Multivalued Dependency muDhina Design

Multivalued dependency breaks yechina chimiro chekare

Mune dhegi yehukama, kuvimba kunowanikwa apo ruzivo rwakachengetwa muhwendefa rimwechete dheedheni rinonyanya kuronga mamwe mashoko akachengetwa patafura rimwechete. Kuvimba kwevanhu vakawanda kunowanikwa apo kuvapo kweimwe kana mitsara yakawanda iri patafura kunoreva kuvapo kweimwe kana mimwe mizere mune imwe tafura imwe chete. Isa imwe nzira, maitiro maviri (kana mapoka) ari patafura anozvimiririra kune mumwe, asi zvose zviri zviviri zvinoenderana nechitatu chiito.

Kuzvidzivirira kwakanyanyisa kunodzivirira kumira kwechimiro chechina chimiro chemazuva ose (4NF). Relational databases zvinotevera zvishanu maitiro akasiyana-siyana anomiririra mazano ekugadzira zvinyorwa. Vanodzivirira kushandiswa kwemaitiro uye kusawirirana mune data. Ichina fomu yekuratidzira inobata nehukama-kune-humwe hukama mu database .

Functional Dependency vs. Multivalued Dependency

Kuti unzwisise kuvimba kwakanyanya, zvinobatsira kuti udzokere zvakare kuti kushanda kunoshanda ndei.

Kana chirevo X chichinyatsogadzirisa chinonzi Y, ipapo Y inoshanda zvichienderana ne X. Izvi zvakanyorwa sa X -> Y. Somuenzaniso, muVadzidzi patafura iri pasi, Mudzidzi_Name anogadza Major:

Izvi zvinoshanda zvinogona kunyorwa: Student_Name -> Major . Mudzidzi mumwe nomumwe_Name anosarudza imwechete Major, uye kwete.

Kana iwe uchida kuti dhesiyo ionewo mitambo iyi vadzidzi vanoitora, unogona kufunga kuti nzira iri nyore kuita izvi ndeyokungowedzera imwe koromo yakanzi Sport:

Dambudziko riri apa ndeyekuti Ravi neBet vachitamba mitambo yakawanda. Zvakakosha kuwedzera mutsva mutsva kune imwe mimwe mitambo.

Iyi tafura yakaratidza kuvimba kwevanhu vakawanda nokuti chikuru uye mutambo zvakasununguka kune mumwe asi asi zvose zvinoenderana nemudzidzi.

Uyu muenzaniso wakajeka uye nyore nyore kuonekwa, asi kuvimba kwevanhu vakawanda kunogona kuva dambudziko mune deta huru, yakaoma yakawanda.

Kuvimba kwakanyanya kune zvakanyorwa X -> -> Y. Munyaya iyi:

Mudzidzi_Name -> -> Major
Mudzidzi_Name -> -> Sport

Izvi zvinoverengwa se "Student_Name multidetermines Major" uye "Student_Name multidetermines Sport."

Kuvimba nevakawanda kunoda nguva dzose zvinokwana zvitatu nokuti zvinoumbwa nezvinhu zviviri zvinodarika chetatu.

Multivalued Dependency uye Normalization

Tafura ine hutano hwakawanda inopesana nehuwandu hwemhando yeChina Chechina Fomu (4NK) nokuti inogadzira zvisizvo zvisingabatsiri uye inogona kuita kuti zvinhu zvisingaenderani. Kuunza izvi kusvika ku 4NF, zvakakosha kuputsa ruzivo urwu mumatafura maviri.

Tafura iri pasi apa yava nehutano hwakanaka hwevadzidzi veNew -> Major, uye hapana maitiro akawandisa:

Kunyange zvazvo tafura iyi inewo kushanda kwakasiyana kwekudzidza kwevadzidzi_mamwe -> mitambo:

Zvakanzwisisika kuti kuongorora kunowanzotaridzirwa nekuita nyore magome akaoma kuitira kuti ave nemashoko akanangana nemumwe pfungwa kana musoro panzvimbo yekuedza kuita tafura rimwe chete ine mashoko akawanda akaparadzana.