[JURIST] Servicemembers Legal Defense Network (SLDN) [advocacy website] filed suit Thursday in the US District Court for the District of Massachusetts [official website] challenging [text, PDF; press release] the federal Defense of Marriage Act (DOMA) [text; JURIST news archive]. DOMA defines marriage for federal purposes as a legal union between one man and one woman. The suit alleges that DOMA unconstitutionally denies gay and lesbian service members equal protection under the law. The suit further alleges that "[t]here is no…