Here is the relational database schema we consider.

Participants$($SiteID $($INT$),$ LastName $($CHAR$),$ FirstName $($CHAR$),$ PatientID $($INT$),$ Status $($CHAR$),$ Gender $($CHAR$),$ Age $($INT$),$ Language $($CHAR$),$ Disease $($CHAR$),$ Ethnicity $($CHAR$))$

AlertPIN$($PatientID $($INT$),$ EndUserID $($INT$),$ AlertName $($CHAR$))$

Events$($EndUserID $($INT$),$ StartDate $($DATE$),$ EndDate $($DATE$),$ EventName $($CHAR$))$

Messages$($EndUserID $($INT$),$ ResponseDate $($DATE$),$ Question $($VARCHAR$),$ Response $($VARCHAR$))$

Readings$($EndUserID $($INT$),$ ReadingID $($INT$),$ ReadingType $($CHAR$),$ ReadingDate $($DATE$))$

Note:

$$Primary keys are underlined.

$$Datatypes are provided for your guidance.

$$Status is either Active or Not Active. Patients are either actively involved in the program or not at all involved.

$$Language is English, French, Hindi, Spanish, Mandarin

$$Ethnicity is Asian, Black, Native American, White

$$EndUserID $($different than the PatientID$)$ is generated for a participant in case of an alert event

$$ResponseDate is the date recorded when a patient is questioned by a doctor$/$ nurse

$$ReadingID generated for every EndUserID for different ReadingType like blood pressure, pulse rate, weight, etc.

Write the following queries in relational algebra, not SQL $($so cannot use aggregation$)$:

$1.$PatientIDs who$$s readings were recorded for blood pressure and oxygen level.

$2.$Names of the black participants who suffer from coronary disease or Alzheimer$$s$.$

$3.$Ids of the patients who have at least $3$ readings recorded on $21$st February $2021(\text{'}02-21-2021\text{'}).$

$4.$Status of the participants for whom an alert was generated and who$$s readings were recorded for weight and sugar.

$5.$PatientIDs of the participants who are active but have no readings recorded.

$6.$SiteID with at least $500$ non$-$active participants.

Solutions :

$1.$ output : patientid $->$ participants

condition : records of blood pressure and oxygen level $->$ readings

join : patientid$($participants$)=$ patientsid$($alertpin$),$ enduserid$($alertpin$)=$ enduserid$($readings$)$

$($participants$.$patientid$)(($Participants $$ participants.patientid$=$alertpin.patientid AlertPIN$)$ alertpin.enduserid$=$readings.enduserid $($ $($readings$.$readingtype $=$ 'blood pressure' $$ readings.readingtype $=$ 'oxygen level'$)($Readings$))$

$2.$ output : patientname $->$ participants

condition : ethnicity $=$ 'black' $,$ suffered from coronary disease $->$ participants

join : query involves only the participants table so no join needed

$($participants$.$firstName, participants.lastName$)($$($participants$.$ethnicity $=$ 'Black' $($participants$.$disease $=$ 'coronary disease' $$ participants.disease $=$ 'Alzheimer$$s$\text{'}))($Participants$))$

$3.$ output : patientid $->$ participants

condition : count $>=3,21$st February $2021(\text{'}02-21-2021\text{'})->$ readings

join : patientid$($participants$)$ and alertpin and readingdate$($readings$)$

participants.patientid $(($$($count$(*)>2)($$($readings$.$readingdate $=\text{'}02-21-2021\text{'}))($Readings$)$ AlertPIN $$ alertpin.patientid$=$participants.patientid Participants$)$

$4.$ output : status $->$ participants

condition : records of weight and sugar $->$ readings

join : status$($participants$)$ and alertpin and records$($readings$)$

$($participants$.$status$)($Participants $$ AlertPIN $($$($readings$.$readingtype $=$ 'weight'$)($Readings$))($$($readings$.$readingtype $=$ 'sugar'$)($Readings$)))$

$5.$ output : patientid $->$ participants

condition : no records, active status $->$ participants $,$ readings

join : patientid$($participants$),$ alertpin, readings

$($participants$.$patientid$)($$($participants$.$status $=$ 'Active'$)($Participants $$ participants.patientid$=$alertpin.patientid AlertPIN$))$ $($alertpin$.$patientid$)($alertpin $$ readings$)$

$6.$ output : siteid $->$ participants

condition : count $>=500,$ non$-$active status $->$ participants

join : query involves only the participants table so no join needed

$($participants$.$siteid$)(($ count$(*)>499)($ status $=$ 'not active'$))($Participants$)))$

please review and make necessary changes if needed. also it is only for relational algebra so now cannot use any sql query in this.