If you need to update a lot of data, I suggest use CSV file, it reduces write much code more than use XML file to insert/update/etc... data in data base, and in my personal opinion insert/update/etc... the data manually it's not the best practice.
For example to insert country state
in data base:
By CSV file:
id country_id:id name code
state_us_1 us Alabama AL
state_us_2 us Alaska AK
state_us_3 us Arizona AZ
state_us_4 us Arkansas AR
state_us_5 us California CA
state_us_6 us Colorado CO
state_us_7 us Connecticut CT
state_us_8 us Delaware DE
By XML file:
<record model="res.country.state" id="state_us_1">
<field name="name">Alabam</field>
<field name="code">AL</field>
<field name="country_id" ref="base.us"/>
</record>
<record model="res.country.state" id="state_us_2">
<field name="name">Alaska</field>
<field name="code">AK</field>
<field name="country_id" ref="base.us"/>
</record>
One record for every data!
I hope this can help you!