```xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns4:query_definition xmlns:ns2="http://www.i2b2.org/xsd/cell/crc/psm/1.1/" xmlns:ns4="http://www.i2b2.org/xsd/cell/crc/psm/querydefinition/1.1/" xmlns:ns3="http://www.i2b2.org/xsd/cell/crc/psm/analysisdefinition/1.1/">
    <query_name>Cefazolin-Cefazolin@15:28:53</query_name>
    <query_timing>ANY</query_timing>
    <specificity_scale>0</specificity_scale>
    <panel>
        <panel_number>1</panel_number>
        <panel_timing>ANY</panel_timing>
        <panel_accuracy_scale>100</panel_accuracy_scale>
        <invert>0</invert>
        <total_item_occurrences>1</total_item_occurrences>
        <item>
            <hlevel>1</hlevel>
            <item_name>Cefazolin</item_name>
            <item_key>\\i2b2_MEDS\i2b2\Medications\MUL\(LME10) anti-infectives\(LME36) cephalosporins\(LME37) first generation cephalosporins\cefazolin\</item_key>
            <item_icon>FA</item_icon>
            <tooltip>medications \ anti-infectives \ cephalosporins \ first generation cephalosporins \ cefazolin</tooltip>
            <class>ENC</class>
            <constrain_by_modifier>
                <modifier_name>Dose</modifier_name>
                <modifier_key>\\i2b2_MEDS\Medication\Dose\</modifier_key>
                <applied_path>\i2b2\Medications\MUL\(LME10) anti-infectives\(LME36) cephalosporins\(LME37) first generation cephalosporins\cefazolin\%</applied_path>
                <constrain_by_value>
                    <value_operator>LT</value_operator>
                    <value_constraint>1000</value_constraint>
                    <value_unit_of_measure>mg</value_unit_of_measure>
                    <value_type>NUMBER</value_type>
                </constrain_by_value>
            </constrain_by_modifier>
            <item_is_synonym>false</item_is_synonym>
        </item>
    </panel>
    <panel>
        <panel_number>2</panel_number>
        <panel_timing>ANY</panel_timing>
        <panel_accuracy_scale>100</panel_accuracy_scale>
        <invert>0</invert>
        <total_item_occurrences>1</total_item_occurrences>
        <item>
            <hlevel>1</hlevel>
            <item_name>Cefazolin</item_name>
            <item_key>\\i2b2_MEDS\i2b2\Medications\MUL\(LME10) anti-infectives\(LME36) cephalosporins\(LME37) first generation cephalosporins\cefazolin\</item_key>
            <item_icon>FA</item_icon>
            <tooltip>medications \ anti-infectives \ cephalosporins \ first generation cephalosporins \ cefazolin</tooltip>
            <class>ENC</class>
            <constrain_by_modifier>
                <modifier_name>Frequency</modifier_name>
                <modifier_key>\\i2b2_MEDS\Medication\Frequency\</modifier_key>
                <applied_path>\i2b2\Medications\MUL\(LME10) anti-infectives\(LME36) cephalosporins\(LME37) first generation cephalosporins\cefazolin\%</applied_path>
                <constrain_by_value>
                    <value_operator>IN</value_operator>
                    <value_constraint>('AC','QD')</value_constraint>
                    <value_type>TEXT</value_type>
                </constrain_by_value>
            </constrain_by_modifier>
            <item_is_synonym>false</item_is_synonym>
        </item>
    </panel>
</ns4:query_definition>

```

I want to find all instances of the medication "Cefazolin" where the dose is less than 1000 mg and the frequency is either "AC" (every other day) or "QD" (every day). This query will search for records within the i2b2 database that meet these specific criteria, focusing on the medication type, dose, and frequency.